Soundly support:
There are two kinds of promo codes: The Coupon code where you must enter your payment information and the Promo code where you don’t need to enter any payment information
If you already have an account, go to user -> profile in the Soundly software and choose Upgrade pick the Pro Monthly option. On the payment page, toggle the Have promo code option and enter your promo code.
If you don’t have an account, register your account, and follow the previous instructions on the payment page.