Connecting to Ringcentral Api

I’m trying to connect to ringcentral’s api which requires an oauth2 flow. I’m using postman to get the login popup to work. Here’s the get new access token setup in postman.

Which generates a popup whereby I input credentials and grant access to the app

I can’t figure out how to get to this part in the api connector. I think it might have to be a 3rd party login service, but I’m not sure of all the fields.

The callback url has to be put in my ringcentral account and match the api call. Here are the reference documents for ringcentral’s api.

Please help. Thanks in advance.