invoice

Thanks to everyone who works on this group
I want to design a sales invoice
The problem I'm facing
The invoice table saves only the first line and does not save the rest of the items in the invoice

To clarify

If the customer buys several things, a book, a pen, a ruler
Only the book and all information about it are saved, but the rest is not

Note: I am using Python - Django MySql
Please help me or post any link that can help me