Allow standard exception to handle strings for JSON API responses

[TechhDan]

Fix: Allow Standard Exception to handle strings

Our company started using this SDK and we noticed that when an object is not found we received a blank exception message. Looking into the code I noticed that the Payment Rails API server is sending back JSON strings with the code and message. However, the Standard Exception does not take into account strings such as this case. The result is that the exception comes out blank. This PR fixes the exception to handle both strings and arrays.

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, create a GitHub Issue in this repository.

[denizaygundev]

Changes look good to me.

I am also experiencing this issue.