There are 3 ways you can invite contributors to a Bubble.
1. When Creating a Bubble:
2. After you have created a bubble: go into your Bubbles tab --> Select a Bubble --> click the Admin Features dropdown --> click Bubble --> select Invite Others
3. Inviting with a Bubble Pin: drill into the Bubble that you would like to invite participants to --> click the Admin Features dropdown --> click Bubble --> select View Bubble Pin