Base page to manage discount codes
Obsolete public modifier
Adding ID and name to the pricing info returned
Simple discount code adding form
HTML5 form treatment

Autofocus on the email field and make the pricing fields explicit number types with upper and lower boundaries.
Method to receive the form POST
Parse the code into an object
Save discount code
Display existing discount codes
Log creating a code into the Audit Log
Display Object info in the Audit Log
Selection to email code automatically
Success message and return to codes list
Check if email not already registered, paid
Code comments

The method will be longer, makes it easier to read the flow.
Adding missing input field ID

Label won't work without it.
Form to reedem code
Validate discount code format
Try reading code from database
Read Registration before redeeming code