Where to find logs about Stripe app install failure?

Question

I have been developing a Stripe app that is current in "test mode" (hasn't been approved, but is available for external testers). It has been successfully installed by several external testers over the last month and the install worked perfectly. As far as I know, nothing has changed since those installs.

When I tried to test installing it on another account of mine yesterday, it failed to even get to my redirect URL and showed:

There does not seem to be any errors in the Stripe developer's console, logs, and it doesn't seem to be hitting my server at all.

How do I debug what's going wrong here? Is there anywhere I can look to figure out what's happening?