API Development

Hi, We are using 24SevenOffice as ERP system with billing, CRM, accounting and stock management. We are a IT business and have started to use HaloPSA as our primary tool. This tool can do everything we have in 24SevenOffice too, so we want them to sync. When we create or edit a customer either in 24SevenOffice or HaloPSA they should update each other so we are running with up to date info everywhere. When we create an order in HaloPSA and set it to ready for invoice we want the order to be sent to 24SevenOffice with status "ready for invoice" and all product lines with correct price and quanty. When the order is invoiced in 24SevenOffice we want the invoice number and payment status to be sent to HaloPSA again. If 24SevenOffice generates any orders to a customer without generating it in HaloPSA first and then invoice it those should also be transferred to HaloPSA. Sometimes we create credit notes. Those will be created in 24SevenOffice and should be transferred to HaloPSA as the other orders so we have status of all orders in both systems. We have tried to create an API that creates the customers in both CRM's and it seems to work. We still need the update part of it.