If you want to earn more coins, you can do any of the following:
Purchase an Adventure Pass to the Wilds.
Find beasties to battle and win the battles.
Sell your purchased items in your backpack back to merchants in the town.
Sell your beasties or beastie eggs.
Complete your teacher's assignments.
Complete Daily Challenges.
Claiming Achievement Rewards.
Participate in the Quizzler Game Show.
Play the Beastly Pizza game.