Getting someone onto a shared trip should take five seconds, not an account-creation flow. So it does.
Scan and you're in
Show your QR code, they scan it with their phone camera, accept the invite, and they're on the shared list. No app switching, no typing in codes.
Or just send a link
Not in the same room? Send the invite link instead, same result. Useful for the family member joining from a different city.