Integration Problem

[nojav-48]

OAuth2 is a very simple authentication, I have integrated many Application like Xero, payment gateways, Google API's etc. but never faced this much trouble integrating. 
Always getting:

Insufficient permissions to fulfill the request.

the provided authorization grant code is invalid or was issued to another client

The requested scope is invalid, unknown, malformed, or exceeds the scope granted to the client

Does any have a clue? or better guide line then ebay developers?

[rony2-31]

Hello, @nojav-48 

The errors you're facing likely stem from mismatched scopes, incorrect grant handling, or client misconfiguration. Here's how to fix them:

Insufficient Permissions: Ensure the requested scopes match the API endpoints. Test tokens using eBay's OAuth Playground.   Maryland Health Connection

Invalid Grant Code: Use the authorization code only once, and exchange it quickly. Ensure the client_id and redirect_uri match those used in the authorization request.

Invalid Scope: Double-check scope names in the eBay Developer documentation and confirm they're included during the authorization request.

Best Regards