Firstly, moved to the appropriate board for this. Be wary next time please.
Secondly to answer your question:
I too was hard-stuck on making this work but with the help of a friend I figured it out.
Essentially, you have to use a unique opener during your multiplayer games. It should show up on here: https://forum.toribash.com/tori_opener.php
You're free to update the name of that specific opener you've just "made" and it should show up in-game almost immediately, the next time you use it.
[7:19 PM] Aliosa: Can't have loopholes if there are no loops.
[9:14 AM] Viddah: Just remember if you step on toes youre gonna have to suck on them to make the pain go away
[9:16 AM] [Faux_fan]ancient: put me in the screenshot