Can one create a payment module using Shopify API https://docs.shopify.com/api ? Can "Shopify app" also be a payment gateway module?
I understand Shopify develop and host any payment gateway module themself, but it seems one could create their own module?
But these hosted modules from Shopify are not updated.
So why can't a third party payment gateway provider can create their own payment module as a Shopify app. Is that possible using the Shopify API?
I think the answer to your question is another question.
If you coded up a working Payment Gateway not currently supported by Shopify, using Active Merchant (which is currently supported), would Shopify accept it, and thereafter would merchants be able to choose it?
That is a tough one. You can try! You might succeed even. All those working Gateways in Shopify did not get there exclusively from Shopify.
Well as of now they are not accepting any payment gateway module. If you talk with higher manager and submit some required documents than there is some hope...
For now, you can create the payment gateway and move the user traffic on your server from cart section.
You will get cart details user details shipping details. NO VAT TAX OR COUPON CODE FUNCTIONALITY WILL WORK.
There is some limitation as i mentioned above. So if you do not have issue with loosing with mentioned functionality you can go ahead.
Yes, it's possible to develop a payment Gateway for Shopify as a private app integration. Our agency has done it in the past. The most recent was the integration of GoPay payment gateway. Czech solution for Czech Shopifyers.
The problem now is that not everybody has access to do it and Shopify closed the possibility of getting those accesses.
You can check the info you are looking for here - https://help.shopify.com/api/sdks/hosted-payment-sdk
