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Keeping track of your customers' payments is relevant in handling your business in QuickBooks Online (QBO). Currently, the feature to apply a vendor credit to a customer credit memo isn't available in QuickBooks Online. Let me give you a workaround to ensure you can add vendor credit to your customers through invoices. 

Utilizing a clearing account to help transfer or apply a vendor credit to customer invoices is the best way to manage this in QuickBooks Online. I'll show you how:

1. Create a Bank account called Clearing Account.

1. From the Accounting menu, click Chart of Accounts.
2. Click the New tab, then choose Bank for the Account Type.
3. In the Account Name field, enter Clearing Account.
4. Select Save & Close.

2. Create two journal entries.

1. Click the +New option, then select Journal Entry under OTHER.
2. Debit the Clearing account (created in Step 1) and credit Accounts Receivable for the amount of sale.
3. Choose Accounts Receivable in the Account row, then enter the customer in the Name field.
4. Create a second general entry. This time, debit Accounts Payable and credit Clearing Account for the amount of the sale.
5. In the Name field on the Accounts Payable row, enter the vendor name that needs the bill credit created.
6. Click Save & Close.

3. Apply the credit to an invoice

1. From the Customer & Leads menu, click Customers.
2. Find the specific customer, then click Receive Payments.
3. Click Set Credits and select the credits to apply.
4. Select Done, then, click Save and close.

Moreover, it's better to consult your accountant for expert guidance about this. They can assist you in managing situations like this effectively. If you don't have one, you may find an accountant through this link: ProAdvisor.

Check out this article to learn how and when to give a credit memo to customers: Create and apply credit memos or delayed credits in QuickBooks Online.

Please get back to us if you have further questions or concerns about handling payments and journal entries in QuickBooks Online. I'm always here to help you. Keep safe!