Hi,

If you directly create invoice from the customer invoice menu, it will not affect the stock. You can see that the product itself is not a required field in invoice. As you need to affect the sales in stock, either you can use following method.

1. Use Odoo POS: this will make the sales better and faster also affects stock and accounting

2. Use sales module itself, create sale order and confirm the sales and create invoice, f the process is lengthy, you can check for the custom addons which will automate this process of validating the stock picking and generating accounting entries. See this module: https://apps.odoo.com/apps/modules/11.0/sale_automatic_workflow/

Another module: Sale Order Automation

3. Another option you can try is directly create stock picking which will reduce the stock and then create the invoice from it, for this you can use this custom addon: https://www.odoo.com/apps/modules/10.0/invoice_stock_move/

Thanks