Which place you joined
This wiki's official game link is place 127932298993998, universe 10770605947, by the group I am eating. Public game metadata cited for that place lists a max of 1 player. A sampled look at public servers of the main place found one player in each server.
A second place ID, 136995587459936, is listed for this same experience under the name Ragdoll Reality multiplayer. Opening that place page shows the same creator and the same description. One write-up sampled its public servers at a cap of 10, with seven to nine players online. Another metadata check did not confirm that cap. If your server panel still says 1, you are in the main place.
How to bring a friend
The main place has no spare slot if the cap is really 1, so an invite there has nowhere to land. Open the multiplayer place from the experience's place list, confirm the server panel shows other players, then invite. An in-game portal between the two places was not confirmed.
What is not known
- PvP rules are not in the description, the event posts, or the public place fields. Older videos can carry a PvP tag. That tag is not a ruleset. The Sandbox pass says it works in solo and PvE servers, which implies more than one server type and still does not say players can damage each other.
- Whether kills, cards, and passes follow you from one place to the other is not published. A shared store is not proof of a shared save. Open the shop in both places and compare one card before you commit to a long grind.