Create a plugin for the main CS platforms (PHP needed)

We need to create the plugins to the following platforms (not all at once - one/two per freelancer)
- Shopify, WooCommerce, WHMCS, Carrd, Typedream, Tilda

The plugin should help the users to use our solution as a processing solution in line with Stripe, Paypal.
The only action they should make: register at our platform (inxy.io) and receive the API keys.

Here is the documentation:
https://documenter.getpostman.com/view/23101517/VUxNS84v

Here is SDK on PHP:
https://github.com/inxy-payments/merchant-sdk