FB message sent but not delivered

[PaintedL4dy]

Can anyone help? I've tried googling but can't make sense of this. I use FB messenger on my laptop, he uses it on his phone. If I've sent a message and it shows as sent but not delivered, what might cause that?

(We are not FB Friends and I do not have another way of contacting him).

If you’re not friends on FB then your message automatically goes into a message request folder and doesn’t notify the other person that they have a message unless they open messenger and see the little red ‘1’ next to the message request folder.

Thank you. We have already exchanged messages on FB, it's my only way of contacting him.

I just need to be patient and accept that all sorts of things could stop a message arriving at his phone. Thanks for replying @PinkFizz1 I was a bit wobbly earlier.