I want to help investigate the emailing issue with your invoice, elogan1.

To start, let's check if the invoice is not set a as recurring transaction for your customer. This could be the reason it was sent multiple times.

Here's how:

1. Go to the Gear icon.
2. Under Lists, choose Recurring transactions.
3. On the list of the transaction, locate if the invoice is included.
4. Click Edit to open.
5. Uncheck the Automatically send emails box.
6. You can also change the Type to Unschedule.
7. Once done, Save Template.

If the invoice is not set as recurring, I'd suggest contacting our QuickBooks Support Team to get this checked and investigated. They're equipped with tools to determine the main cause of this. I'll guide you how.

1. Click the (?) Help icon.
2. Select Talk to a Human.
3. Enter an invoice email multiple times and press Enter.
4. Click I still need a human.
5. Select Contact Us to connect with our live support.
6. Choose Get a callback.
   

Also, you can customize your invoices before sending them to your customers. This helps you create sales forms that match your brand and make it more professional-looking.

Keep me posted if you have further concerns sending invoices in QuickBooks. I'll be on the lookout for your response. Have a good one.