Is there is any Document that gives a complete set of characters not supported by DocuSign in file names/envelope payload?
Filename of the file which is sent for signature had spaces or special characters gives INVALID REQUEST BODY error.
This has nothing to do with DocuSign, you have to have valid JSON. If it's not valid JSON, it won't allow you to make API calls.
Other than that there are rules specific to the field.
*** Spaces are allowed for names, email subject, but not email address and filename.**
There are cases when characters (like quote) have to be encoded either for the JSON or XML or SMTP or whatever other protocol being used.