Copy the invitation from the lobby
The host creates a private room in the Android game. Use Copy Code in the lobby and send the six digits to invited friends. The code is not a web download link or an account recovery code. Share it privately so unexpected players do not join your group.
Enter all six digits
On another device, open Join Room and enter the complete code from the host. Check it against the current lobby, especially if an old invitation was forwarded. Correcting a mistyped code can solve an invalid invitation; it cannot reopen a room that has already closed or expired.
Identify the actual obstacle
A full room needs an available seat. A closed room needs a new invitation. For a network timeout, restore your connection and retry the current code. Do not keep generating random codes. If the correct invitation repeatedly fails, give support the time and error shown; share room details privately.