"Invalid platform app" error using Instagram Basic Display API
If you are using Postman, do remember it's a POST request. Use form data
I ran into this same issue. Problem was I was using the Facebook App ID and App Secret instead of the Instagram App ID & App Secret. You must go to the "Instagram Basic Display" section on the Facebook developers site then scroll down until you find the Instagram App ID & Secret.
When you exchange the code you need to use a POST request.
From the looks of your url, you've formed it as a GET request with all the parameters as part of the url rather than as form data. Try sending the parameters as part of the post body instead