Does QuickBooks automatically send an invoice receipt once the customer has paid ?

I know some information regarding payment receipts, Zack. 

In QuickBooks Online (QBO), you'll receive a payment receipt automatically once your customer pays the invoice. However, creating and sending receipts to them is unavailable. Instead, you'll need to send it manually by going to the Sales menu and finding the specific invoice. From there, you can send the receipt to your customer. 

Here's how: 

1. Go to the Sales menu located at the left navigation panel and click Invoice.
2. Click the Dropdown under the Action column. 
3. Choose the Send option. 
4. In the Email body field, you can change the message and enter what you prefer to say to your customer. 
5. Once done, press Send. 

You can also personalize and add some specific info to your sales forms by using this article: Customize invoices, estimates, and sales receipts in QuickBooks Online. 

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