You can define a setting to help the control of your bills. Bill Control lets you choose if the supplier sends you the bill before or after you receive the goods.
For this feature to work, go to: Purchases --> Configuration --> Settings and select which way you want to control your bills.
Change the control policy
While the setting above will be your default method of bill control, you can always select which way you want to invoice your product on each product page under the Purchase tab.
You might want to use different settings for different types of products.
Verify your Vendor Bill
If you didn’t receive any of your product yet on Purchase Order under the Shipment tab,
Depending on the billing policy defined above. If you're supposed to be billed based on ordered quantity, Odoo will suggest a bill for the number of units ordered.
If you're supposed to be billed based on the received quantities, Odoo will suggest a bill for 0 as shown above.