You can add products in your online store to an invoice easily, Just follow https://fatora.io/ar/user-guide/%D8%A5%D8%B6%D8%A7%D9%81%D8%A9-%D9%85%D9%86%D8%AA%D8%AC-%D9%84%D9%84%D9%85%D8%AA%D8%AC%D8%B1-%D8%A7%D9%84%D8%A5%D9%84%D9%83%D8%AA%D8%B1%D9%88%D9%86%D9%8A/ that guides you on how to do it.