The given client credentials were not valid. Please modify your request and try again.
The error message you’re seeing typically indicates that there might be an issue with the credentials you’ve entered. Please double-check that you have entered the correct FedEx account credentials without any typos, spelling mistakes, or unnecessary spaces, especially if the credentials were copied and pasted.
Additionally, ensure that you are not using test credentials in the live environment or vice versa.
You may try creating a new FedEx account with a news REST API credentials, as it’s possible that the current one has some limitations.
If after verifying your credentials they are correct, and you’re still facing this issue, it would be best to contact FedEx Customer Support for further assistance. They may need to check the status of your API access on their end.