Hello there, CYCLOPEDIA. 

The steps provided by my colleague are for QuickBooks Desktop which only supports the United States, United Kingdom, and Canada users. If you are using QuickBooks Online, on the other hand, the option to add a column in your invoice sales form is unavailable. 

You can use one of our supported third-party apps as suggested by my colleagues. You can click here to visit our QuickBooks App page. I'll be attaching the article provided above on how to handle sales forms and customize them: Customise invoices, estimates, and sales receipts in QuickBooks Online.

Feel free to post again if there's anything else that you need help with. Take care!