problems integrating with the Calendly API

I'm working on integrating Calendly with an omnichannel system. During authentication tests through Postman, I was successful in receiving the authentication token. However, when making other requests, I consistently receive error 500 - Internal Server Error. I would like to check if I am making any mistakes in the token request or in other subsequent requests

Attached, 'Print 1' shows my OAuth2 request, in which I successfully obtained an authentication token. However, when using this token in 'Print 2', another request, I receive the mentioned error.