Add functionality to the site on Wordpress. Today

Hello)

Now there are:

1. Website (sell vitamins) made on WP Woocommerce
2. On the site, payment is not made through Woo a directly through the API in Strype. Via core php. That is, we receive the "paid/not" token directly.
3. Paid orders are added to the users account.

What you need to do:
1. On the checkout page add input [ promo code]
2. Create promo codes in the database (you can use your hands or a plugin)
3. Now that user A used the code XXXXXX, he received a 10% discount from his total.
4. and user B received a credit of $20 if user A used the code XXXXX

Conditions:
1. User A can use the code only once
2. User B can use the code for which he receives money 0 times