There are three ways to join a bubble:
2. If the owner of the bubble has selected to allow participants to invite others (under the Bubble Privacy Settings: see where this is when you are creating a new bubble on your phone, OR when you are creating a new bubble on the web) a bubble participant can also invite you.
3. There is a third way to join, but it is not used as often and that is the manual PIN entry for Bubbles. If you have a bubble’s pin, you can join a bubble with that pin without having been invited to the bubble.
Go to the My Bubbles tab --> click the Join Bubble button --> Enter Bubble PIN and click Join the Bubble in the top right corner
Enter the Bubble Pin to join the bubble.
How To Invite Participants To A Bubble/Join A Bubble With A Pin