diff --git a/x-pack/agent/pkg/fleetapi/client.go b/x-pack/agent/pkg/fleetapi/client.go
index ed6cb510aacb..724f780a05ba 100644
--- a/x-pack/agent/pkg/fleetapi/client.go
+++ b/x-pack/agent/pkg/fleetapi/client.go
@@ -59,17 +59,17 @@ func init() {
 
 // NewAuthWithConfig returns a Kibana client that will:
 //
-// - Send the AccessToken on every HTTP request.
+// - Send the API Key on every HTTP request.
 // - Ensure a minimun version of Kibana is required.
 // - Send the Fleet User Agent on every HTTP request.
-func NewAuthWithConfig(log *logger.Logger, config *config.Config, accessToken string) (*kibana.Client, error) {
+func NewAuthWithConfig(log *logger.Logger, config *config.Config, apiKey string) (*kibana.Client, error) {
 	return kibana.NewWithRawConfig(log, config, func(rt http.RoundTripper) (http.RoundTripper, error) {
 		rt, err := baseRoundTrippers(rt)
 		if err != nil {
 			return nil, err
 		}
 
-		rt, err = NewFleetAccessTokenRoundTripper(rt, accessToken)
+		rt, err = NewFleetAuthRoundTripper(rt, apiKey)
 		if err != nil {
 			return nil, err
 		}
diff --git a/x-pack/agent/pkg/fleetapi/client_test.go b/x-pack/agent/pkg/fleetapi/client_test.go
index 85aebf55417b..28e383392b15 100644
--- a/x-pack/agent/pkg/fleetapi/client_test.go
+++ b/x-pack/agent/pkg/fleetapi/client_test.go
@@ -21,11 +21,11 @@ import (
 )
 
 func TestHTTPClient(t *testing.T) {
-	t.Run("Access Token is valid", withServer(
+	t.Run("API Key is valid", withServer(
 		func(t *testing.T) *http.ServeMux {
 			msg := `{ message: "hello" }`
 			mux := http.NewServeMux()
-			mux.HandleFunc("/echo-hello", accessTokenHandler(func(w http.ResponseWriter, r *http.Request) {
+			mux.HandleFunc("/echo-hello", authHandler(func(w http.ResponseWriter, r *http.Request) {
 				w.WriteHeader(http.StatusOK)
 				fmt.Fprintf(w, msg)
 			}, "abc123"))
@@ -36,7 +36,7 @@ func TestHTTPClient(t *testing.T) {
 			})
 
 			client, err := kibana.NewWithRawConfig(nil, cfg, func(wrapped http.RoundTripper) (http.RoundTripper, error) {
-				return NewFleetAccessTokenRoundTripper(wrapped, "abc123")
+				return NewFleetAuthRoundTripper(wrapped, "abc123")
 			})
 
 			require.NoError(t, err)
@@ -50,6 +50,30 @@ func TestHTTPClient(t *testing.T) {
 		},
 	))
 
+	t.Run("API Key is not valid", withServer(
+		func(t *testing.T) *http.ServeMux {
+			msg := `{ message: "hello" }`
+			mux := http.NewServeMux()
+			mux.HandleFunc("/echo-hello", authHandler(func(w http.ResponseWriter, r *http.Request) {
+				w.WriteHeader(http.StatusOK)
+				fmt.Fprintf(w, msg)
+			}, "secret"))
+			return mux
+		}, func(t *testing.T, host string) {
+			cfg := config.MustNewConfigFrom(map[string]interface{}{
+				"host": host,
+			})
+
+			client, err := kibana.NewWithRawConfig(nil, cfg, func(wrapped http.RoundTripper) (http.RoundTripper, error) {
+				return NewFleetAuthRoundTripper(wrapped, "abc123")
+			})
+
+			require.NoError(t, err)
+			_, err = client.Send("GET", "/echo-hello", nil, nil, nil)
+			require.Error(t, err)
+		},
+	))
+
 	t.Run("Fleet user agent", withServer(
 		func(t *testing.T) *http.ServeMux {
 			msg := `{ message: "hello" }`
@@ -81,9 +105,13 @@ func TestHTTPClient(t *testing.T) {
 	))
 }
 
-func accessTokenHandler(handler http.HandlerFunc, accessToken string) http.HandlerFunc {
+func authHandler(handler http.HandlerFunc, apiKey string) http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
-		if r.Header.Get("kbn-fleet-access-token") != accessToken {
+		const key = "Authorization"
+		const prefix = "ApiKey "
+
+		v := strings.TrimPrefix(r.Header.Get(key), prefix)
+		if v != apiKey {
 			http.Error(w, "Unauthorized", http.StatusUnauthorized)
 			return
 		}
diff --git a/x-pack/agent/pkg/fleetapi/round_trippers.go b/x-pack/agent/pkg/fleetapi/round_trippers.go
index 17898c1eb858..0f8a904e2484 100644
--- a/x-pack/agent/pkg/fleetapi/round_trippers.go
+++ b/x-pack/agent/pkg/fleetapi/round_trippers.go
@@ -11,6 +11,9 @@ import (
 	"github.com/elastic/beats/agent/kibana"
 )
 
+// ErrInvalidAPIKey is returned when authentication fail to fleet.
+var ErrInvalidAPIKey = errors.New("invalid api key to authenticate with fleet")
+
 // FleetUserAgentRoundTripper adds the Fleet user agent.
 type FleetUserAgentRoundTripper struct {
 	rt      http.RoundTripper
@@ -31,27 +34,35 @@ func NewFleetUserAgentRoundTripper(wrapped http.RoundTripper, version string) ht
 	}
 }
 
-// FleetAccessTokenRoundTripper allow all calls to be authenticated using the accessToken.
+// FleetAuthRoundTripper allow all calls to be authenticated using the api key.
 // The token is added as a header key.
-type FleetAccessTokenRoundTripper struct {
-	rt          http.RoundTripper
-	accessToken string
+type FleetAuthRoundTripper struct {
+	rt     http.RoundTripper
+	apiKey string
 }
 
 // RoundTrip makes all the calls to the service authenticated.
-func (r *FleetAccessTokenRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
-	const key = "kbn-fleet-access-token"
-	req.Header.Set(key, r.accessToken)
-	return r.rt.RoundTrip(req)
+func (r *FleetAuthRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
+	const key = "Authorization"
+	const prefix = "ApiKey "
+
+	req.Header.Set(key, prefix+r.apiKey)
+	resp, err := r.rt.RoundTrip(req)
+
+	if resp.StatusCode == http.StatusUnauthorized {
+		defer resp.Body.Close()
+		return resp, ErrInvalidAPIKey
+	}
+	return resp, err
 }
 
-// NewFleetAccessTokenRoundTripper wrap an existing http.RoundTripper and adds the accessToken in the header.
-func NewFleetAccessTokenRoundTripper(
+// NewFleetAuthRoundTripper wrap an existing http.RoundTripper and adds the API in the header.
+func NewFleetAuthRoundTripper(
 	wrapped http.RoundTripper,
-	accessToken string,
+	apiKey string,
 ) (http.RoundTripper, error) {
-	if len(accessToken) == 0 {
-		return nil, errors.New("empty access token received")
+	if len(apiKey) == 0 {
+		return nil, errors.New("empty api key received")
 	}
-	return &FleetAccessTokenRoundTripper{rt: wrapped, accessToken: accessToken}, nil
+	return &FleetAuthRoundTripper{rt: wrapped, apiKey: apiKey}, nil
 }