Yes, you can add fields to the invoice template in the online version of odoo. You'll wanna use odoo studio, a really handy tool for customizations without diving into code. Head to your invoice template in odoo and activate studio. It gives you a neat drag and drop interface to add fields.

Since you're looking to include the due date based on net payment terms, you'll likely need to add a related field pulling from the payment terms on your invoice. In studio, create a new field, ands et it to link to the payment terms due date.

But hey, it's not all smooth sailing. Without a deeper understanding of the relationships and database structures in your specific odoo setup, it could be a bit tricky. Trust me, odoo's logic here can be weird sometimes. odoo documentation and community forums can help if you hit a wall. Don't be afraid to experiment, but backup your data or test in a sandbox to avoid unwanted stress!

Hi,

It is possible to extend the invoice model and add a new field through Studio. You can refer to the link below to add a field.

https://www.cybrosys.com/odoo/odoo-books/odoo-15-studio/build-an-app/creating-models-and-adding-fields/

Hope it helps