Connect an existing Booking site to an existing Paymentwall gateway (+mobile responsive)

I already have a booking system, run professionally by a company with good IT staff. I also have a payment gateway, already setup, already fully functional (already 'live' and tested on existing website), it is with Paymentwall (a company 10fold than paypal which also accepts bank-to-bank payments, they mostly facilitate companies in gambling industry). Our service is non-gambling, but administrative agency only. As you can read on our booking system, they offer a way to "connect" it to any paymentgateway, and even propose a script (which will send product specs and amount to be billed), read the short script here: [login to view URL] Our booking widget (the one that needs to be connected to Paymentwall) is here: [login to view URL] As you can see, it currently has a few 'pay' buttons. One is meant to go to Paymentwall, but is not connected yet. Paymentwall does offer both mobile and non-mobile payment platfrom (just like paypal does). We have 2 options: client goes on beds24 --> redirect direct to Paymentwall gate OR client goes on beds24 --> beds 24 'packages the Cart specs, like amount due, persons etc' --> this cart data is sent to our site in a way that our site basically 'takes over the Cart info' (our site already has paymentwall plug working on it) --->pays DIRECTLY paymentwall gate We pay on delivery only. We had some very bad experience with half finished products so far and will not make this mistake again. Time should be dedicated 100% to us during project, eg, we have no understanding for freelancer spending time in hospitals, attending to 'other urgencies', not willing to work till late to finish project on time, or not responding on skype. Hence, we pay on completion.