Custom code to integrate subscription to a payment gateway

Hello I need a developer to integrate my subscription website to a payment gateway.
This means that the customer subscribe to a monthly or 3 months plan and this allows them to view the content on the site.

The gateway has provided an api on how the code should be written:

https://directpayonline.atlassian.net/wiki/spaces/API/overview
https://directpayonline.atlassian.net/wiki/spaces/API/pages/32702465/verifyToken+V6

Test account credentials:
Company Token: 9F416C11-127B-4DE2-AC7F-D5710E4C5E0A
Services types:
3854-Test Product
5525-Test Service

Endpoint: https://secure.3gdirectpay.com/API/v6/

PaymentURL: https://secure.3gdirectpay.com/payv2.php?ID=token