Qonto module for WHMCS

[Giancarlo Di Massa]

I would like to integrate Qonto in WHMCS. Qonto is a bank that has a simple JSON Rest API that can be used to check balances and download transactions data (payments by customers). I would like the module to perform those operations:

- be available as a payment method "bank transfer" (actually this is a very simple module that just outputs a text with bank coordinates)
- periodically check the bank server for updates (I would like to use Saloon PHP v3 for the API calls, or something around Guzzle)
- display to the administrator incoming money transfers in the admin area
- match transfers to invoices to mark those as paid

I tracked two possible paths for that:
- a third payment gateway, this would allow me to use the transactions feature of WHMCS to have a ready made table of transactions and even populate them to match with invoices
- leaving the very simple "bank transfer" module that I already have as a payment gateway and creating instead an "addon" module that shows an interface to the administrator

I am for the first route, it seems more integrated, however:
- not all the incoming transactions will be matched by an invoice in WHMCS, would that be OK?
- is the user able to go to the Billing / Transactions panel to a transaction without an associated invoice, and by inputting the invoice number setting that invoice as paid manually (manual matching)?
- is it possible to send an email each time a transaction is created by the payment gateway, telling the administrator that either A) it has been matched to an invoice number, setting it as paid, or B) it didn't find a matching invoice to match?
- I found a stub here to help my IDE PhpStorm https://raw.githubusercontent.com/oblakhost/whmcs-stubs/master/whmcs/whmcs.php is this the best one you know of?

This code is planned to be released for free as open source on the marketplace and supported as needed. I am more of a Laravel/Symfony programmer so some of the questions may seem trivial for some. Thank you in advance.