What to tell guests, and where to put it
Pick one address to be the star and keep it consistent. On the card, print the subdomain form or the QR beside a short line; in the group chat, paste the app link because it fits in a sentence without breaking. Whichever you use, it opens the same page, so a guest who scans a card in spring and a guest who taps a message in autumn both land on the current version.
You do not need anyone to memorise the address, which is the reassuring part. The link or code does the finding, so the invitation's job is only to point clearly. A legible, tapable doorway beats an invented clever one every time, and it stays true while you edit the day behind it.