You can either use the session-wide link, persistent links, or single-use links.

Session-wide link

If it is impractical to distribute distinct URLs to each participant, you can give the following start URL to all 4 participants.

https://floating-sierra-61355.herokuapp.com/join/rafc9hj4a8/

Note: unlike the other link modes, this does not prevent the same person from playing twice.

Persistent links

If you want to give your participants permanent links that don't change, you should create your session in a room.

Single-use links

Below are single-use links, which you can distribute to your participants. Each link has a unique code for the participant.

P1	https://floating-sierra-61355.herokuapp.com/InitializeParticipant/owjakvrl
P2	https://floating-sierra-61355.herokuapp.com/InitializeParticipant/868jeojn
P3	https://floating-sierra-61355.herokuapp.com/InitializeParticipant/kd0nd3p1
P4	https://floating-sierra-61355.herokuapp.com/InitializeParticipant/b0t1ni8p