Thanks for sharing this with us, @Dynobrit.

It appears that you require a feature that matches your expectations. I'm here to share how to submit feedback to our developer in QuickBooks Online.

Since adding a discount per item within the invoice isn't available, we can send product suggestions to them. 

Here's how:

1. At the top, click the Gear icon, then hit the Feedback button.
2. Fill in the box with your comments or product suggestions. Then click Next to submit.

Once done, your feedback will go to our Product Development team to help optimize your QBO expertise. 

I also encourage visiting our QuickBooks Blog page from time to time to stay current on the latest news and updates about QBO.

Additionally, if you need to organize and keep track of your customers as your industry expands. Here's a guide on how to add customers and keep your customer list up to date: Add and manage customers in QuickBooks Online.

Drop me a message if you still need concerns within your QBO account. The Community is always here to assist you. Take care.