Suggestion:
1) Users have to define an item with no stock maintenance for service-related activity. For this an item(service) should be created with Stock Option as ‘0’ flag for Inventory control. 0 value is for ‘Not stock maintenance’.
2) A Purchase order (PO) is an authorized order from a purchasing agent or department to an external vendor/supplier to supply the service and maintenance work. All tax calculation and terms & conditions will be entered here.
3) Users have to use the Purchase receipt transaction to receive materials and services from Purchase orders.
4) Users have to create a Purchase payable Voucher against Purchase order for supplier bill amount .