This is really well made! I know from my experience building Cakedesk [1] that the requirements of invoices vary greatly from country to country and from user to user.
Some things you can add to appeal to more people that are useful to most:
* Keep track of clients and personal info so the user doesn't have to type the address / invoice IDs every time
* Allow users to keep track of which items are paid/unpaid
* Allow users to declare sales tax on the invoices
* Allow users to upload their own HTML-based invoice designs
* Allow users to add subitems to items
Good luck with the project, it looks well-made and it will be useful for many people!
Some things you can add to appeal to more people that are useful to most:
* Keep track of clients and personal info so the user doesn't have to type the address / invoice IDs every time
* Allow users to keep track of which items are paid/unpaid
* Allow users to declare sales tax on the invoices
* Allow users to upload their own HTML-based invoice designs
* Allow users to add subitems to items
Good luck with the project, it looks well-made and it will be useful for many people!
[1]: https://cakedesk.app