Unable to install apps on Shopify Plus stores (red banner)

I am working to get an app approved. Weirdly enough this is my 3-4 app I have submitted and the app review team is having an issue installing my app, specifically on Shopify Plus stores. On the install page instead of the banner being orange it is red and the install button is disabled.

Before I push back I was wondering if anyone had any suggestions as to why Oauth would work on non Plus stores and not Plus stores?

I think it might be that they are testing an unapproved app on a Shopify Plus store which has a paid plan and is not on a developer plan.

Any and all thoughts appreciated.

Best,
Chris

It ended up being the error on behalf of the app tester.