Bonus coins may not be used for tipping.
Coins bought in the Coin Shop or earned by watching video ads or completing other special offers may be given as tips, but bonus coins received for signing up, inviting friends, or in Inbox gifts may only be used to unlock episodes.
When viewing the Coin Shop or when trying to tip a creator, tap/click the (?) next to your coin balance for a breakdown of coins bought and earned, versus bonus coins.
Learn more about coins and how to buy or earn them for tipping.