You can set a Minimum Order Amount when you are creating a new Price Sheet, or updating an existing Price Sheet for your Store. Any Collections using that Price Sheet will require clients to meet this minimum amount in order to checkout. By default, the minimum Order amount for each Price Sheet is $0.00.
To change or add a Minimum Order amount, go to Store Dashboard > Products and click the Edit/Pencil icon beside the name of the Price Sheet you'd like to change.
If your client tries to checkout without reaching the minimum order amount you've set, they will see an error message: