Azure Logic Apps Custom Connector: Reply URL

We are trying to make an Azure Logic Apps Custom Connector that just adds a record to Business Central.

I made an App Registration so that I could get a Client ID and Secret. If I use postman with OAUTH 2.0, I can do a GET/POST successfully.

I changed the Authentication Type in the Azure Logic Apps Custom Connector's security tab to OAuth 2.0. I have Generic Oauth 2 set as the Identity Provider.

I have filled in the Client ID, Client Secret, Auth URL, Token URL, and refresh URL. The Redirect URL is already set up for you.

I have ensured this matches the value within the App Registration.

However when I attempt to authorize and test the connection I receive the following error:

Please could anyone advise on what I may have missed.