To apply a coupon code, or make any changes in the billing section of an account, you need to be logged in as the owner of that account.
Here are the steps you need to follow to apply your coupon code to your Proto.io account:
1. If you do not have an account with Proto.io, proceed with creating one from the following link: https://proto.io/en/signup/
2. Sign in to your account and go to the Billing section from the upper right 'Manage Subscription' link in the account drop-down menu.
3. If you do not have an activated account then proceed with your subscription activation.
4. Select a plan from the options listed (Monthly or Annually). Some coupons are only issued for specific plans.
5. Fill out your account information and check the 'I have a Coupon' option to enter your Coupon Code. Click 'APPLY'.
6. Coupons usually apply a discount to the total amount. In the case that you have a coupon that applies 100% discount (i.e. complementary account) then you do not need to fill out the credit card details.