This Odoo apps automatically create invoice from Picking when picking(Shipment/Delivery) get Done. This module also comes with multiple configuration option i.e Auto Validate invoice from Picking, Auto send invoice by Email when Picking Done. Whenever Delivery order or picking will done this module create customer invoice/vendor bills automatically same as sales and purchase order product price with delivered and received quantity. If you activate auto validate option then when delivery/shipment get done its automatically creates customer/supplier invoice and validate it automatically. Same for send by email option, If you activate Send by Email option then when delivery/shipment get done its automatically creates customer/supplier invoice and Send it same as send by email function. User can have option to activate both option together and in this case when picking will become done it will create invoice , validate it and send it to customer/supplier.

Configuration

Under Invoicing > Configuration > Settings enable "Automatic Validate Customer Invoice from Delivery" and "Auto Customer Invoice send by Email" to auto validate and send invoice by email to user.  

Creation of Customer Invoice

After confirming the sale order delivery order will created.

Delivery Order

After validating delivery order invoice will automatically created for delivered quantity of the product.  

Customer Invoice

User can see invoice is validated automatically.  

Customer will get auto invoice email on delivery validation.