Hi,
I have no experience with xero, but I check the document, it implements webhook, and the example is quite clear, create/update contact, create/update invoice
I often do webhook using laravel for payment gateway. from simple invoice to quite complex one (android apps - laravel - create invoice - send back to android for payment, and check if payment already made, not instant, but later, or tomorrow, then send notif to android that the invoice is paid).
I believe I can do this project