Issue
When attempting to create a review app, users are faced with an error stating: Couldn't create this review app Your role on the team is not allowed to perform that action.
Resolution
Review apps are always created on behalf of the Heroku account that initially connected the parent app to Github. To resolve this, make sure that the user who set up Github sync is listed as an admin on the team so they have sufficient permissions to create review apps.
If you don't want to change the role of that particular account, then you can disconnect the app from Github and reconnect it with a team admin account.