Hi Stiofan,
Thanks for your reply.
We would like to manage, generate invoices and receive payments from once central system. Which in this case is WHMCS. It makes it much easier and gives us much more control.
We cannot have invoices generated with different numbers to our WHMCS system. Our WHMCS is also already integrated with XERO as our accounting system. We have also already setup a full payment gateway with WHMCS.
Hope this makes sense. Your help with which API/Hooks to use from GEO will be greatly appreciated.