Hello, first of all thank your help.

I understand how to invoice two sales orders on a single invoice, but my question is about the custom fields created with Odoo Studio.

In Sales Order "SO001" I have a custom field (say, as an example) ABC with the following information: "A123"

... and in Sales Order "SO002" I have the same custom field "ABC" with the following information: "B456"

The "ABC" field was included in the invoice format. The problem is that when I invoice two sales orders, only one of the two "ABC" fields is included.

I would need the two codes to come out like this:
✔ ABC: A123, B456   

✘    ABC: A123

 What does come out correctly are the Sales Order:
✔    Sales Order: SO001, SO002