Skip the word 'app'

The moment someone hears 'app,' a certain kind of relative mentally checks out, expecting a download, a password, an account. Say 'scan this and take a photo like normal' instead, because that's literally what happens.

Show, don't explain

Scan the code yourself in front of them and hand them the phone mid-shot. Watching someone else do it for three seconds teaches more than a paragraph of instructions on a table card ever will.

Put it somewhere they're already looking

A code they have to search for defeats the point. Put it on the table right in front of their seat, not in a corner of the room they'd have to be told to find.

One sentence, not five

“Scan the code, take a photo, that's it” is a full and complete explanation. Anything longer starts to sound complicated even when it isn't.

Why this matters more than it seems

The whole appeal of a browser-based camera is that it doesn't require anyone to be good with phones in the first place. If the instructions end up sounding like a tech tutorial, something about the setup, not the guest, is the problem.