Add-on Can anyone help with an extension to Xen Product Manager

Hello, Developers.
Tell me, please, how and who to ask for writing extension modules for Xen Product Manager?
This add-on works with PayPal and respectively with Stripe by @Liam W.

Because in country Ukraine the payment system is not working. But there is an similar LiqPay.
Detailing for PHP developers.
Who'll help to expand opportunities for XPM?