When i send a facebook message reply back to someone on my phone it says it has sent but the person doesn't receive it on there chat
I have the same issue. Garmin told me first that it is a Facebook issue, then that it is fixed in Connect 5.8. It isn't.
I tend to believe that it is Facebook as id I try to send a like from the notification on the phone then it is not sent either. I reported it to FB but no feedback in the last two weeks. I think Garmin should also report a ticket towards FB.