We are also having this problem.
We have two apps registered with AppStoreConnect. One of them all of a sudden is failing to install on device, thought the deployment to TestFlight succeeds. I can't yet any information as to why its failing to install.
Just the dialog on device with this message: Could not install : The requested app is not available or doesn't exist.
All builds for this app are now failing to install in the same way, even builds that previously have succeeded.
I have tested on various iPads, iPhone 12 mini and tvOS. Have tried to add, remove and re-add test groups and install attempts at each step. Have tried changing the test details message and install attempt afterwards.
This app is in the 'Prepare for Submission` state on ASC, with a yellow icon.
Topic:
App Store Distribution & Marketing
SubTopic:
TestFlight
Tags: