Google Ads API Single Client Integration
I am currently trying to integrate single Google Ads account for my client using RestSharp in C# (don't want to use client libraries). I have found the useful link to generate access token by providing client ID , Client secret and Refresh token.
https://developers.google.com/google-ads/api/docs/rest/auth
I am now trying to test on Postman first before I start developing code in C# but failing to get access token. The screen shot below shows the call I am doing to get access token using Post man. 
I also tried CURL in postman which was mentioned in the link above but getting the same error.
FYI it is a Desktop app chosen in google console to generate client ID and secrete because I will be creating console app to integrate Google Ads API.
Use Google OAuth 2.0 playground. (note: you have to have Web application for that)
It generated developer token for me after changing web application from desktop. Thanks. However, when sending end point request, I am getting another error "message": "The caller does not have permission", "status": "PERMISSION_DENIED", "details": [ "authorizationError": "DEVELOPER_TOKEN_NOT_APPROVED" }, "message": "The developer token is not approved. Non-approved developer tokens can only be used with test accounts."
I believe it is because I am using production account and my developer token is currently enabled for test account.? in ads profile it says: Your developer token is currently enabled for Test Account Access. Apply for Basic Access in the "Access level" section to begin interacting with production accounts.