This is probably a lot more work than you're willing to put in, but the Facebook Messenger bridge for Matrix has actually been reliable, set'n'forget, and heada

This is probably a lot more work than you're willing to put in, but the Facebook Messenger bridge for Matrix has actually been reliable, set'n'forget, and headache-free for me, whenever I have to use it for Marketplace. I wouldn't otherwise mention it, but this is one of the few sites where "Stand up your own messaging server" isn't a completely insane suggestion.