Well I guess they are sending you purchase orders and requesting invoices because they cannot use credit card because of corporate rules(accounting, policies et

Well I guess they are sending you purchase orders and requesting invoices because they cannot use credit card because of corporate rules(accounting, policies etc). Its possible to automate this. You should use some ERP system or even accounting system. You could read automatically the purchase orders they send to you and create sales order's, deliveries and invoices in the ERP system. Are you even using accounting system? Maybe the software you are using has the possibilities to create this kind of integration?