How to ad UNIT of the items

Welcome to the Community, @info-aljurof-com.

Thank you for reaching out to us with your concern about adding units of the items.

Currently, QuickBooks Online doesn't have units in measurement. As a workaround, you can customize the looks of an invoice and change the Quantity into a unit.
 

Here's how: 

1. Go to the Gear icon ⚙ and then select Custom Form Styles.
2. Click the New Style.
3. Select the Invoice.
4. Go to Content.
5. Click the Edit button on the middle portion of the invoice where you can find the items.
6. Click EDIT LABELS AND WIDTHS.
   
7. Change the name of the Quantity into a unit of measurement that you want.
8. Select Done.

You can also check on how to create and edit custom fields in QuickBooks Online Advanced for more customization options.

Feel free to reach back out to me if I can be of more help with customize option in QuickBooks Online. I'll make sure to get back to you as soon as I can.