Hi Frederik, you can add a response validation for order amount or order quantity field. Calculate order amount Login to Neartail > click on the form to open it > Edit page will be displayed > In the Neartail Edit page, click on the Add price field button > select Order Amount, click Next > select Standard calculation using TOTAL() formula, click Next > click Create > Order amount field will be added in the form > click on the gear icon next to this field > Field settings page will be displayed > click Answer > click Configure link for the validation option > select Number, Greater than option, enter 0 and click Save. If the order amount is zero, then it will show an error when the customer tries to submit the order. Calculate orde quantity In the Neartail Edit page, click on the Add field button > enter the title "Order Quantity" > click on the gear icon next to the Order Quantity field > Field settings page will be displayed > click Answer > enter the QUANTITY() formula in the Calculate option > click Configure link for the validation option > select Number, Greater than option, enter 0 and click Save. If the order quantity is zero, then it will show an error when the customer tries to submit the order. Please try this and confirm.