I introduced Xooloo Messenger, which is made for children, to our family with great success. However, my device is forbidden when I want to join.
Regain your privacy! Adopt /e/OS the unGoogled mobile OS and online services
if you can extract a logcat from the time window (a few seconds) when the device sees the decline it’s a hint to what’s happening: [HOWTO] log app errors with LogFox on-device to create bugreports
You can also show it to the publisher of the app.
(on at tangent: Threema Messenger can block anyone that isn’t in the system contacts, something the other mainstream messengers do not offer. Gives some assurance for families / kids)