I've been getting this error when opening TestFlight since this morning.
I tried restarting the network, re-install testflight, updating my iPhone, and re-logging with my Apple ID.
This error prevents me from installing or updating all apps linked to my account, so I don't think it's related to a particular app permission.
Topic:
App Store Distribution & Marketing
SubTopic:
TestFlight
Tags:
Feedback Assistant
TestFlight
Testing