Unexpected message within Mail App

I was just checking my emails this evening on my iPad Pro and this message (see screenshot below) unexpectedly appeared at the bottom of the screen. It only appears within the mail app. It says “Contact from iOS app | DID: 251907”. I can’t get rid of it (I’ve tried restarting my iPad but it is still there). I don’t know why it has suddenly appeared or what it is referring to. I’ve tried googling it but can’t find any information about it. I have never seen it before today. Does anybody know why it is there or what it means? It doesn’t appear in the mail app of my iPhone XS, only my iPad Pro. I don’t want to click on it in case it is malicious.