I am trying to setup my custom app on Zapier partner dashboard using Oauth2.

I have provided/setup all information correctly using their documentation for Oauth2. But if fails when I try to test it using the “Test your Authentication” area.

I added some logs to my backend to trace the API calls. So it follows the below steps :

1. Zapier makes a GET /authorise request, which redirects the user to our webapp login page
2. User authenticates on our webapp and then confirms/consents to the authorisation request
3. Our backend issues a valid “Authorisation Code” to Zapier for it to ask for “Access Token” using the “Authorisation Code”
4. Zapier sends a POST /token request to get the access token and valid “Access Token” is returned
5. And then immediately Zapier again sends a /token request, this time as GET request and not POST, and as expected our backend returns a 405 error as GET method is not supported for /token request.

So I am wondering why Zapier is adding the extra GET  call for /token request? Is there anything I am doing wrong from the setup point of view?