Facebook messenger has extremely sensitive filters. It seems to block most links I try to send. Most recently, I tried to send a GIF of a beautiful city on a river to my girlfriend. Nope, blocked. The link was a GIF sharing site, I don't remember which one, but it's highly unlikely there's any malware on it so it must be a porn filter. And as for sending links to my staging site to a couple of tech friends... forget about it.