I M P O R T A N T
The below information is for web developers or those onboarding kasssh.com with their PHP driven back-end servers. If you're not technically (web) minded, or would rather not be, then please check out widgets | plugins. We naturally respect any merchant (or shop) wishing to write/develop their own back-end solution and to integrate with their P S P.
We hope the below information will save you some time as we have existing and functional solutions, so we'd rather you follow our lead to save you time, but how you choose to do this is your call and as bespoke as you like.
P H P
We are quite agnostic when it comes to the server back-end, but given that 80%+ (and that's a high number) of commercial servers use PHP for their backend, this is a good place to start. Equally, if you use another platform (OK language) such as Python, Go, Java etc. then there is very high chance that you'll know P H P.
We appreciate that your P H P will use a framework (Laravel, Symphony, CodeIgniter, Cake etc.) and we hope you do. We'll cover this with Laravel as this is the No #1 framework in use right now and this is, or should be, easily translated to your platform of choice.
As discussed: kasssh.com needs a Webhook or URL to fire off a payment with your P S P. That is just a URL/Link and you will need that in your routes/api (routes/web.php or routes/api.php if you use Laravel). For the sake of simplicity we'll assume you are going to have a special Controller (/App/Http/Controllers/KassshPaymentController.php) to handle this. That is quite an ASK of you, but better to keep this code or `route` seperate.
The below example (Laravel) has a single line in your routes/web.php or routes/api.php and this should be a POST route (security) and this then follows through to the actual Controller or code. The route will clearly have your https://domain/.... prefix outside of this server code and this should be used as a setting in your Store. (The Payment back-end URL as we call it = a private and secure URL/Webhook which is called when a customer pays over CASH to make good on their shopping cart).
routes/web.php | routes.api.php
The above example is suggesting a receipt to Stripe (as your P S P) with a URL of `.../payments/kasssh/receive-to-stripe` and a controller method/function called stripePayment which exists in a Controller called KassshPaymentController.php. Again (stress) this is a for web /devs !
For the sake of this page, that's enough to start with and to see how this translates to `real` code then you should look at the relevant examples on a more case-by-case basis, e.g. integrate kasssh/Stripe with Shopify. They are listed on the L H S menu.