Hi there, @LewLew81.

Currently, there's an ongoing investigation (INV-86502) about getting a delivery error when attempting to send invoices in QuickBooks Online (QBO). As a workaround, you can follow the recommended steps below. 

• You can save the invoice form as a PDF and send it via email through your business or another email address.
• You can send your customer a link to their invoice or estimate through WhatsApp by following the steps described in the Send Invoices with WhatsApp article.
• You can send your customer a link to their invoice or estimate through SMS or messenger service. Simply click on Save and Share link then select Copy link and paste it into your SMS or messenger service.
• If you have a Gmail or G-suite email account, you can use the Send with Gmail feature to send QBO forms from your own address following the steps in the Use your Gmail address to send invoices article.

While we don't have the exact time frame for when this will be resolved, I recommend reaching out to our Phone support team to add you to the list of affected users. Once done, you'll be able to receive updates and news about the resolution. Here's how:

1. Select the Help icon and choose the Search tab.
2. Then, click Contact Us.
3. From there, enter a brief description of your concern and select Continue.
4. Next, choose either the Call back or Chat option to get in touch with our support team. 

I'll include this helpful resource that you can use as a guide in case you need to customise your invoice templates: Customise invoices, estimates, and sales receipts in QuickBooks Online.

I'm always here ready to lend you a hand if you have any other concerns managing your invoices in QuickBooks. Have a good one and stay safe.