To fix a failed invoice email:

1. Make sure the invoice is no longer Draft - draft invoices cannot be sent.
2. Check that the customer record has the correct email address.
3. Open the invoice detail page and review the delivery status or any error shown there.
4. Verify your email delivery setup in Workspace Settings → Email Delivery.
5. If the customer still does not receive it, ask them to check spam or junk and then send the invoice again.

Tip: Preview the invoice first if you want to confirm the correct customer and document before resending.