Facebook has had some issues today relating to DMs on Messenger and Instagram, which caused message to send to fail and as of writing, everything is back up and running but it was down from 09:30AM BST / 04:30AM ET and came back up this afternoon.
Facebook spoke to The Verge today and said:
“Earlier today, some people have experienced trouble sending or receiving messages on Messenger, Instagram or Workplace Chat. The issue has since been resolved and we apologize for any inconvenience.”
This didn’t seem to affect Facebook’s main service or WhatsApp.