Hi there, @aspenmerk.
You can check the history of your invoice to verify if it was sent to your customer. Let me guide you how.
In your QuickBooks Desktop (QBDT):
- Go to the Customers menu.
- Click the Customer Center.
- Select the appropriate customer.
- Double click the invoice to open it.
- Click the See History link to see the status of the invoice.
I got you this article for more details: Verify that an invoice was emailed and read by recipient.
You can also contact your customer and verify if they receive the invoice you sent to them. Also, I encourage you to check this resource if you want to give a unique look to your invoice: Use and customize form templates.
Do leave a comment below if there's anything I can help you with. I'd be ready to help you anytime.