I can help you with applying the discount to your invoices, @Ffraga.

You can use a clearing account to transfer or apply a vendor credit to customers' invoices. I'll show you how.

Here's how to set up a clearing account:

1. Go to the Lists menu and click Chart of Accounts.
2. Right-click anywhere in the Chart of Accounts then choose New.
3. Once you are in the Add New Account window, choose Bank then select Continue.
4. In the Account Name field, enter Clearing Account.
5. Click Save & Close.

Then, create two journal entries:

1. Go to the Company menu and click Make General Journal Entries.
2. Debit the Clearing account you created earlier and credit Accounts Receivable for the amount of sale.
3. In the Name field on the Accounts Receivable row, enter the customer name created in QuickBooks Desktop.
4. Click Save & New.
5. Create a second general entry. This time, debit Accounts Payable and credit Clearing Account for the amount of the sale.
6. In the Name field on the Accounts Payable row, enter the vendor name that needs the bill credit created.
7. Click Save & Close.

Once done, you can now apply the credit to your invoice:

1. From the Customer menu, select Receive Payments.
2. Select the invoice.
3. Click Set Credits and select the credits to apply.
4. Select Done.
5. Then, click Save and close.

You can check out these articles for more information about creating a clearing account and applying credit to your invoices:

• Set up a clearing account
• Record an invoice payment

Here's more information on how you can resolve common issues when applying a payment towards an invoice for multiple payment methods, reapplying, refunding payments, and more. 

I'm always here if you need more help recording your transactions. I'm always here to help. Have a great rest of the day!