You can get the code by clicking on “download now” and downloading “PREMIUM_CODE_v1.4.txt” which is a text file that contain the code. No need to pay again. Thanks for your support.
When you bought the game, you received a mail from which you can download the file “PREMIUM_CODE_v1.4.txt”. If you have lost this mail, go to this page: https://itch.io/docs/buying/already-bought