Server-to-Server OAuth App Returns Error 124 Invalid Access Token Despite Valid Credentials

I have a Server-to-Server OAuth app that is activated and live on my account. When making API calls I receive error code 124 Invalid Access Token. I have verified my Account ID, Client ID, and Client Secret are correct and have regenerated the Client Secret multiple times. The app has the following scopes: meeting:write:meeting:admin, meeting:read:meeting:admin, user:read:user:admin, webinar:write:webinar:admin, webinar:read:webinar:admin. Please help me identify why the token is invalid.