When you have a need to disable a payment for a form (either temporary until next promo session or during low periods in business), let's process it this way:
1). Login to emailmeform.com with your account credentials.
2). Hover over the form you need to disable payments, select "Options", then click the "Payments" button.
3). Uncheck "Enable Payment" and save the form.
Please note, in case you've already deleted all price-enabled fields on the form, you'll need to add any price-enabled field back, then save the form and only after that you will be able to disable payments for the given form.