In QuickBooks Online when I create an invoice and try to send an email, with QuickBooks Payment, it show a total of all the customer's open invoices and not just the one.

Welcome to the Community, @bweston. I'm here to ensure only one invoice balance will show when sending an email.

Let's take a look at your invoice template in your QuickBooks Online account. You may have selected the Show on invoice box which causes the total of all customer's open invoices to display on the page.

To fix this, please follow the steps below:

1. From the left panel, choose the Sales menu and select Invoices.
2. Click the transaction and select Edit invoice.
   
   
3. Choose the Customize button and click Edit current.
   
   
4. Select the Content tab and choose the body of the invoice.
5. Under Account Summary, uncheck the box next to Show on invoice.
6. Lastly, click Done.
   
   

Then, proceed in sending your invoice again. For detailed steps, please see this article: Manage invoice in QuickBooks Online.

Additionally, let me share these links that you may find relevant in personalizing and handling your sales forms: 

• Customize invoices, estimates, and sales receipts
• Record invoice payment

That should get you back on track. Feel free to post again if you have further questions about sending invoices. I'll be around to help you.