API codes should be written on classic asp page. — 2

I need payment system created by API and script should be written in Classic Asp.
Codes should be clean and there should be instruction how to implement the script myself to my own website’s payment page.

Could be simply 3 pages:

payment.asp : payment button will be here, visitor click and goto payment screen.
paymentdone.asp : once payment completed, visitor will be forwarded to this page. This will be my Instant Payment Notifications page customers will able to only reach if the payment successfully completed. This page shouldn’t be accesable unless the payment was done.

I also need simple instructions telling about where to put codes to implement to my own webpage.

OPEN SANDBOX ACCOUNT HERE:
https://account-sandbox.nowpayments.io/dashboard