This is how my naive solution is so lucky! The plan is to use a URL to generate the initial message, so not being able to see the PM interface is a bonus!
That’s pretty fine too, as this is basically doing the same thing as using a Google form would be. It’s mostly for a one-way initiation of a conversation. I should check what happens if someone replies to the PM, though.
Ah, yes. The Royal “We”. Thanks very much for your help. You’ve taught me a lot and I appreciate it.