API integration and copying

We want a integration between the accounting system at; <[login to view URL]> and the billing system at <[login to view URL]> We want the API to be built in PHP. WHMCS is a ordering/billing system that creates their own PDF bills when a order is made into the system. We do our accounting through E-conomics which means that we need to do double the work to move it over. The optimal would be to make these two system share some information regarding; costumers personal information, bills and if the bills are paid or not. The goal is: When a bills is created by someone in the MHMCS system (no matter if it new or old) the bills will be copied to the E-conomic system for the costumer to see. If it is a new costumer that the bill is regarding the costumer personal information should be moved as well. When a bill is marked as paid in WHMCS it shall be marked as paid in E-conomics as well. When a bill is marked as paid in E-conomics it shall be marked as paid in WHMCS as well. Here is the WHMCS program, with that and the API from E-conomics you should be able to figure out if you can programm this or not, and how much it would cost. Here is the download link for the program; [login to view URL] You can use the E-conomics 14 days trail if you need to find out more about it.