Tipping is how free members leave comments on a creators posts. If you do not have a paid membership to a particular creator, you'll have limited access to their DM's and/or comments and a tip is the only way to unlock those features.
We've designed Sunroom this way to ensure creators are chatting to, and interacting with members who are investing in their time/efforts.
By upgrading to a paid membership of a creator, you will no longer have to tip to comment; that's one of the many perks to being a paid Member!