Customer paid us by mistake, and wanted us to transfer the money to the vendor. How to record it?

I'm here to guide you as to how you can record a transfer of payment from your customer to a vendor in QuickBooks Online (QBO), @wldn527.

When you've mistakenly received a customer payment that's intended for another vendor, you'll need to create a Journal Entry (JE) for your Accounts Receivable (A/R) and Accounts Payable (A/P) transactions. Here's how:

1. Go to the + New button.
2. Select Journal entry.
3. Choose the A/R account on the first line from the Account field and enter the amount in the Debit column. Then, choose the customer name in the Name field.
4. On the next line, select the A/P account and enter the amount in the Credit column. Then, choose the vendor name in the Name field.
5. Check the amounts. Make sure the Credit and Debit columns are in balance.
6. Enter information in the Memo section to know why you made the journal entry.
7. Select Save and close or Save and new. 

Once you're done, make a Bank deposit to record the payment to A/R. Then, create a Check or Expense to A/P so you can transfer the money to the appropriate vendor.

Finally, link the deposit payment (through Receive Payment) and A/P expense transaction (through Bill Payment) to the JE. You can create a dummy bill to link your expense transaction to the JE and delete it after. Please see the screenshots below for your reference. This way, you can record the funds based on the actual events.

Then, pull up reports (i.e., Journal, Transaction List by Customer, and Transaction List by Vendor) to verify that all transactions are recorded appropriately. To do this, go to the Reposts menu's Standard tab.

Also, I'd recommend reconciling your accounts every month. This way, you can effectively manage your income and expenses and detect any possible errors accordingly. For the step-by-step guide, you can refer to this article: Reconcile an account in QuickBooks Online.

Please don't hesitate to keep me posted on how it goes in the comments below. If you have other concerns about managing customer payments and vendor transactions in QBO, I'll gladly help. Take care, and I wish you continued success, @wldn527.