In the Admin Panel, under Configure Site, you will find the options to create validation rules for the Cart. Minimum dollar amount validation will be enforced for orders when the roles have been selected.
Once you select one of the roles to turn on this validation, below you will be able to select the minimum order amount for the validation to pass for the Cart. This is helpful to drive larger orders for your customers and to reduce the logistics of many small orders that might be coming through.
If you have any additional questions, please contact firstname.lastname@example.org