diff --git a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ApiClient.cs
index 11f158d6943c..3c817d1a646f 100644
--- a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -370,12 +370,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/RequestOptions.cs
index 8cbf48a60320..6ebad92d9470 100644
--- a/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/others/csharp-netcore-complex-files/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ApiClient.cs
index ab6f1f72507d..96ed4f895950 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -370,12 +370,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/RequestOptions.cs
index 7a1d5b97a887..68cd16375903 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-ConditionalSerialization/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ApiClient.cs
index b6d9195b3f6c..997930301f65 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -277,10 +277,12 @@ HttpContent PrepareMultipartFormDataContent(RequestOptions options)
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var content = new StreamContent(fileParam.Value.Content);
-                    content.Headers.ContentType = new MediaTypeHeaderValue(fileParam.Value.ContentType);
-                    multipartContent.Add(content, fileParam.Key,
-                        fileParam.Value.Name);
+                    foreach (var file in fileParam.Value)
+                    {
+                        var content = new StreamContent(file.Content);
+                        content.Headers.ContentType = new MediaTypeHeaderValue(file.ContentType);
+                        multipartContent.Add(content, fileParam.Key, file.Name);
+                    }
                 }
             }
             return multipartContent;
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/RequestOptions.cs
index 91a5fbf28f3a..70b67cb25906 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-httpclient/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, FileParameter> FileParameters { get; set; }
+        public Multimap<string, FileParameter> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, FileParameter>();
+            FileParameters = new Multimap<string, FileParameter>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ApiClient.cs
index 6f26226ea86b..ffb05840d5bb 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -371,12 +371,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/RequestOptions.cs
index 7a1d5b97a887..68cd16375903 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-net47/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ApiClient.cs
index 6f26226ea86b..ffb05840d5bb 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -371,12 +371,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/RequestOptions.cs
index 7a1d5b97a887..68cd16375903 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient-net5.0/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ApiClient.cs
index ab6f1f72507d..96ed4f895950 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -370,12 +370,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/RequestOptions.cs
index 7a1d5b97a887..68cd16375903 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClient/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ApiClient.cs
index 6f26226ea86b..ffb05840d5bb 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -371,12 +371,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/RequestOptions.cs
index 7a1d5b97a887..68cd16375903 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClientCore/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ApiClient.cs b/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ApiClient.cs
index 62f6adbb205e..bf0d74136153 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ApiClient.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/ApiClient.cs
@@ -370,12 +370,15 @@ private RestRequest NewRequest(
             {
                 foreach (var fileParam in options.FileParameters)
                 {
-                    var bytes = ClientUtils.ReadAsBytes(fileParam.Value);
-                    var fileStream = fileParam.Value as FileStream;
-                    if (fileStream != null)
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
-                    else
-                        request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    foreach (var file in fileParam.Value)
+                    {
+                        var bytes = ClientUtils.ReadAsBytes(file);
+                        var fileStream = file as FileStream;
+                        if (fileStream != null)
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, System.IO.Path.GetFileName(fileStream.Name)));
+                        else
+                            request.Files.Add(FileParameter.Create(fileParam.Key, bytes, "no_file_name_provided"));
+                    }
                 }
             }
 
diff --git a/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/RequestOptions.cs b/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/RequestOptions.cs
index c6b3ccc38f22..b21e8c5ffcdd 100644
--- a/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/RequestOptions.cs
+++ b/samples/client/petstore/csharp-netcore/OpenAPIClientCoreAndNet47/src/Org.OpenAPITools/Client/RequestOptions.cs
@@ -46,7 +46,7 @@ public class RequestOptions
         /// <summary>
         /// File parameters to be sent along with the request.
         /// </summary>
-        public Dictionary<string, Stream> FileParameters { get; set; }
+        public Multimap<string, Stream> FileParameters { get; set; }
 
         /// <summary>
         /// Cookies to be sent along with the request.
@@ -67,7 +67,7 @@ public RequestOptions()
             QueryParameters = new Multimap<string, string>();
             HeaderParameters = new Multimap<string, string>();
             FormParameters = new Dictionary<string, string>();
-            FileParameters = new Dictionary<string, Stream>();
+            FileParameters = new Multimap<string, Stream>();
             Cookies = new List<Cookie>();
         }
     }