Messenger not working

Presumably you are not referring to the Apple Messages App - but instead a third-party App installed from the App Store.

Try deleting the App from your iPad - and then performing a forced-restart:

Delete apps on your iPhone, iPad, and iPod touch - Apple Support

Force restart iPad (models with Face ID or with Touch ID in the top button)

If your iPad doesn’t have the Home button, do the following:

1. Press and quickly release the volume button nearest to the top button.
2. Press and quickly release the volume button farthest from the top button.
3. Press and hold the top button.
4. When the Apple logo appears, release the top button.

Force restart iPad (models with the Home button)

Press and hold the top button and the Home button at the same time. When the Apple logo appears, release both buttons.

After restarting the iPad, re-install the Messenger App from the App Store.