I have tested successfully a debug version of an instant app that is called by an app link, e.g., https://domain/?q=1234567. I have created a release version and signed it with a "Create new" key. Upload to a new Closed Testing release fails, however, because the Bundle is signed "with the wrong key".
What am I doing wrong in trying to test a release version without Publishing publicly? Do I have to go forward to Publish and rely on my previous debug testing of the app link or is there a way to verify the app link operation in closed testing?"