Hello there, @Serge01.

I have some insights to share with you on how you can set up discounts in QuickBooks Online so you will no longer enter them manually.

You can turn on the discount feature in the system so you'll be able to apply discounts for your vendor's early settlement.

Here's how:

1. Click on the Gear icon at the top.
2. Select on Account and Settings.
3. Refer to the Sales menu.
4. Choose Sales form content. 
5. Put a check-mark on the Discount box. 
6. Click on Save.
7. Hit on Done.

After that, you can now use the discount field in your sales transactions.

To do that:

1. Press on + New at the left pane.
2. Select on Invoice.
3. Add the products and services. 
4. Select on Discount percentage or Discount value to enter the discount as a percentage or a specific amount.
5. Enter the amount you want to discount in the discount field.
6. If you want to discount the total before you calculate sales tax, select the arrow icon next to the discount field.
7. Hit on Save and send or Save and close.

You can also use this link as your reference in this set up: Add a discount to an invoice or sales receipt in QuickBooks Online.

Lastly, here are some articles that can guide you in recording customers payments and customizing sales forms in QBO, in case you need them in the future:

• Record invoice payments in QuickBooks Online
• Customise invoices, quotes, and sales receipts in QuickBooks Online

I've got your back if you need further assistance, Serge01. Have a good one!