Messenger links from Facebook not working

Hello everybody

first I should explain that I've been an Android user for many years and I'm a comparative noob to Apple/IOS having recently bought an IPad Pro to replace an aging Asus ZenPad, so I'm still getting to grips with the differences in the way things work.

But I've hit a major issue concerning Facebook & Messenger for IPad....

Scenario: I'm following a thread on one of the Facebook groups I subscribe to and I want to send one of the posters a private message via Messenger.

I don't know this person, they are not in my contacts and our paths have never crossed.

So, just as in Android I tap their name in one of the posts they have made in this particular thread and their Facebook profile page comes up (see edited pic below)

There is a Messenger button (red arrow) so I tap that.

Now...on Android this opens a blank message already addressed to that person, all ready for the text. So you type away, and send. Job done in moments.

But this doesn't happen on the IPad.

Tapping the messenger button just opens up my Messenger Chats, with no link to the poster.

So how do I send this person a PM via messenger? I don't wish to add them as a Facebook friend, nor do I want to add them as a contact, I just want to send them a one-off message relevant to the particular thread we are both following.

There is obviously a way to do it but its got me beat, so any assistance would be really appreciated.