This is another common problem that many people face with Facebook Messenger on their Android. If you are also one of them then you can solve this problem by following the given steps:
1. Open the Settings of your phone.
2. Select the Apps or Apps & notifications option.
3. Tap See all Apps.
4. In the app list, select Messenger.
5. Select Storage & cache.
This can help you to fix your problem.

For more read - https://onlinegeeks.net/facebook-messenger-not-working-on-android-iphone/