Error 931 indicates that the Authentication Token used in your XML or SOAP call was not recognized by the eBay Web Services authentication framework as a valid token. There could be several root causes that trigger a 931 error:
Please make sure you using the token against the correct environment. For example: sandbox user token has to be used against Sandbox environment. Sandbox token will NOT work if used for Production environment.
The token string you have entered is invalid. Check to make sure you have included the full token string, that you received via your Authentication and Authorization process.
Verify the characters in your token are valid. If your token contains any other characters than those listed below, it may have been corrupted:
a to z, A to Z, 0 to 9
Asterisk, Slash, Plus ( * / +)
If you are obtaining tokens via the Redirect method, make sure you are correctly url-decoding your token.
In very infrequent cases, an operational issue within eBay could cause a valid token to be rejected with error 931 as invalid. In this scenario, please retry your request.