The parameters are attached to the link, and the app parses them to find the user. However, the link will be relatively long.
Discussion
How does it limit to 1 invite?
The one-time keypackage shared by the inviter is stored locally and marked there. Once an invitee uses it and sends a group creation request, it is marked as used. If another person tries to use it afterward, the request will be rejected.
More importantly, the one-time keypackage is only included in the link and is never sent to the relay.