We appreciate you letting us know that the email address is correct, info2181.
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Alternatively, if the issue persists, contact our live support team directly. They have the resources to examine the cause of why you're currently experiencing this matter.
For now, consider downloading the invoice as a PDF and sending it manually.
Here's an article you can refer to learn about processing invoice payments: Record invoice payments in QuickBooks Online.
You can hit the Reply button below if you have more questions about sending invoices.
