Passing level 4-20

I entered level 4-20, joined a room that was fighting the boss at the haunted cliffs, and we won. However, this did not open up level 4-21 for me.

How do you get that opened up? I did not receive any stars for the victory; do I need at least one to pass it?

[support1]

As long as you pass the level, you can enter the next one. We will test it. Thanks!

As long as you pass the level, you can enter the next one. We will test it. Thanks!

We need some answers here too:

viewtopic.php?f=504&t=14731

Thanks

I have since tried the level again and beat the boss and now 4-21 is open to me. Maybe a glitch?