Getting error message stating that the invoice was not delivered to the recipients. Please help

Let's perform some troubleshooting steps to get past the undelivered invoices in QuickBooks Online (QBO), Bryantramone.

An email fails to deliver if the email address is incorrect or it could be there’s a temporary issue with the recipient's email server. Let's make sure we associate the right email address to all of your customer accounts. This helps us ensure they'll receive their invoices and pay you on time.

On the other hand, we are unable to identify which of many recipients the invoice was sent to and failed to reach. To see when the invoice is undelivered to your customer, just follow the steps below:

1. Go to Sales, on the left side menu. 
2. Select All Sales or Invoice.
3. In the Status column, you’ll see if the invoice is undelivered or sent.

This indicates that the status will be Undeliverable if the invoice cannot be sent to one of the three recipients. Once done, ask the customer to check their junk or spam folders (if their email address is accurate and they haven't received the email). We can also check your email address in the program which might be causing the issue. Here's how: 

1. Go to Customer & leads, then select Customers.
2. Choose the customer who didn’t receive the invoice.
3. Tap Edit.
4. Check the email address and edit it if needed.
5. Resend the invoice.

You can check out this article for more troubleshooting tips for undelivered emails: 3 solutions for you when customers aren't receiving your emails. Furthermore, I have included some helpful articles that provide further insights about managing your sales transactions:

• Customise invoices, estimates, and sales receipts in QuickBooks Online.
• Set up and send progress invoices in QuickBooks Online.

If you have questions about managing your invoices or other QuickBooks-related concerns, feel free to drop a comment below. I'll be here to help you out. You have a good one.