When i do in house invoicing, customer are receiving emails stating they need to pay the same invoice. How and why is this happening and how do I fix it?

I've got you covered, chris229.

When you send an invoice to a customer, make sure to mark the invoice closed and paid once you receive the payment. This is to avoid confusion and prevent you from resending it.

From the Received payment page, you can choose and link the invoice to mark the transaction as paid. To do this:

1. Go to the + New at the left panel.
2. Choose Receive Payment.
3. Select the name of the customer from the drop-down menu.
4. From the Outstanding Transactions section, select the invoice that you’d like to apply the payment.
5. Choose the payment method.
6. Enter the Reference no. and Memo if applicable.
7. You can either deposit the money to your transaction account or to the Undeposited funds account.
8. Hit Save and close.

For additional information, you can click this article: Record invoice payments in QuickBooks Online.

Another instance would be to check if there is a recurring invoice set up the reason why invoice information is the same and was sent on different dates. You'll want to delete it if you think it's unecessary.

To learn more about managing scheduled transactions, see this article: Edit a recurring template.

However, if you're referring to duplicate invoices sent to your customer, you can review your sales by following the steps below:

1. Go to Sales and select All Sales.
2. Select the No. column to sort it.
3. When the Sales populate, it toggles the numbers in ascending and descending order.
4. Check for duplicates. (If there is, you can void or delete them).

With this article, you can learn more about customizing, attaching files, and emailing sales forms to your customer within QuickBooks Online: Email and customize sales form.

You're always welcome to comment below if you have other concerns or follow up inquiries about managing transactions in QBO. I'm just around to help. Take care always.