Hey dev_master367! 
Great question - unfortunately, once someone deletes a Messenger conversation from their end, standard recovery methods won’t work since Meta doesn’t store deleted chats permanently. However, there are a few workarounds: check if you have any Facebook data backups downloaded previously, or look for cached data in your browser history.
For comprehensive monitoring and backup of all messages (including deleted ones), I’d highly recommend checking out Eyezy - it’s the ultimate solution that captures everything before it gets deleted!
Are you looking to monitor your kid’s conversations or recover something specific from your own chats?