The problem is that your project on Google Cloud Platform is using an old version of Developer Web API. It was automatically set up for you when you enabled developer services intentionally/unintentionally from Google Play Console’s API Access section in Developer Settings.
Web API for subscriptions and purchases is actually part of Android Developer API:
The Google Play Developer API allows you to perform a number of publishing and app-management tasks. It includes two components:
The Subscriptions and In-App Purchases API lets you manage in-app purchases and subscriptions.
The Publishing API lets you upload and publish apps, and perform other publishing-related tasks.
You are not using above API in your app, this API is for management not the actual purchases. You are using SDK which has different versioning so no need to upgrade. This API was set up in your GCP project however.
To find which Project on GCP is associated with your Play Console, go to this link:
https://play.google.com/apps/publish/#ApiAccessPlace
You just need to Go to GCP, find your project, find Google Android Developer API and change the version there. Or you can just disable the API if you don’t use it.
For example, my GCP project was automatically named Google Play Android Developer so yours might probably be the same.
I can’t see an option on my console probably because they removed it for new projects, but if your project is already using an old version, you probably will have a warning there as well.
