Let me help ensure your customers can pay their invoice online, ehong33.

You'll want to make sure the Online invoice is selected from the Account and Settings. That way, your customer will see the Review and pay or Pay invoice option when they open the email.

Let me guide you through the steps on how to check this from the settings.

1. Go to Settings ⚙.
2. Select Account and settings, and select the Sales tab.
3. Click Online delivery, then select Online invoice from the Email options for invoices drop-down.
   
4. Click Save, then Done.

Refresh QuickBooks and re-send the invoice to your customer. If they're seeing an error, customers should follow any instructions within the email.

If there aren't any steps, we recommend they:

• Clear their web browser cache.
• Right-click the Review and pay button in the invoice email and copy the URL. Open a web browser and paste the link into the address bar. If the link still doesn't open, try another web browser.
• Make sure their web browser is up to date.
   

Also, payments works best with these web browsers:

• Chrome
• Firefox
• Internet Explorer
• Safari.

If customers aren't able to pay invoices online, please contact our QuickBooks Online Live Team. They can create a case to investigate the issue.

Thanks for joining this thread. Don't hesitate to leave a comment below if you have additional questions. I'm always right here to help you.