I do work with different branches of the same organisation. I have recently allocated a payment to the wrong invoice. How can I correct this?

Welcome to the Community, @galwaytraining-g. I want to ensure you'll be able to link the payment to the correct invoice in QuickBooks Online (QBO). 

Let me discuss the details on how to get this done.

To fix this, you'll have to delete the payment linked to the invoice. If you had matched the transactions from the banking screen, this will automatically move the payment back into the For Review tab where you can apply it to the correct invoice. Here's how:

1. Go to the Sales menu and choose Invoices.
2. Next, look for the invoice and open it. 
3. Then, click the 1 payment made link shown in the top-right part of the form.
4. Select the date to open the payment. 
5. From here, click the More button and choose Delete to remove the payment.
6. Click Yes to confirm the action.

Once done, apply the payment to the correct invoice. For reference, feel free to check this article: Record invoice payments in QuickBooks Online.

I've also added this resource that you can use as a guide in modifying the details of your sales forms. Doing this not just helps you create attractive forms but also to control what information to display. For detailed instructions, see this article: Customise invoices, estimates, and sales receipts in QuickBooks Online. 

Please let me know how the steps go. I appreciate any updates you can provide. If you have additional questions about managing invoice payments, feel free to leave a comment below. I'm always around in the Community to lend a hand. Have a good one and take care.