We've reported this issue to our engineers for those users using the Canada and International versions, morrismd1.

Our Technical Team is currently investigating the root cause of this issue, to fix it as soon as they can. While a resolution is not yet available at this time, you may want to call us. We'll add you to the list of the affected users, so you'll be notified when there's an update on this issue.

Here's how to get our contact number:

1. Go to this link https://help.quickbooks.intuit.com/en_CA/contact.
2. Select QuickBooks Online.
3. Click the Contact QuickBooks Online Support topic and get the phone number.
4. To reach out to our international support, change the region in the upper right-hand corner. Since they don't have a phone support, you can send an email instead. They'll get back to you within 24-48 hours.
5. In the Please select your country window, choose your region. If it's not in the options, select International below the All other countries section.
6. Select QuickBooks Online.
7. Click the Managing Your Money topic, and then choose Invoicing & Sales Receipts sub-topic.
8. Scroll down and click the Send Email button.

If you're using the US version, you can check the Invoice List report before emailing the invoices to your customers. This way, you'll know if they were already sent or not, to stop the duplicates.

Here's how:

1. Click Reports on the left panel.
2. Type Invoice List in the search box.
3. Click the Customize button in the upper right-hand corner.
4. Maximize the Rows/Columns section, and then click the Change columns link.
5. Check the box for Sent.
6. Click Run report.

Please keep me posted if you need anything else. Thanks.