Create a functions in Laravel - connecting towards two API

I need functions created with guzzle in laravel, where it will check for new payments in "Klarna" (API) since last check was done. And these payments will then get matched with invoices from Fortnox (another API) and POST/PUT (+ add fee from klarna into a so calledd "write off" in fortnox) these OR give out a list of invoices that could not be matched and why.

https://developers.klarna.com/api/
https://developer.fortnox.se/documentation/resources/invoice-payments/


DEADLINE
I usually don't set a small deadline for projects, but for this one I really need this to be completed before 7/10, 2019.