If you have a promo code for Debitoor, you can enter it on the payment page. Please be advised that discount codes are only valid on new subscriptions. Please follow these steps:
Go to "Settings" > "Plans & Pricing"
Choose "Monthly" or "Yearly" pricing from the top
Select the plan you'd like to purchase
On the payment page, you'll find the promo code field on the lower left side of the payment page
Enter the coupon code in the space provided and then click 'Apply'. Make sure that the discounted price is shown prior to clicking "Pay Now".