You can set a minimum amount that a client must spend before they are able to check out in your Store.
To change or add a minimum order amount, go to Store Dashboard > Products and click into the price sheet you'd like to add a minimum order amount to.
While viewing the price sheet, click Settings in the top right hand corner.
Then, under Minimum Order Amount, enter your preferred minimum amount and click Save.
If your client tries to checkout without reaching the minimum order amount you've set, they will see this message preventing them from proceeding: