It's great to see a new face here in the Community. Let's work together and fix the problem you're having when a customer is trying to open an invoice that was sent to them via email.
If your customer is pulling up their email within a browser, I recommend using a different browser. Certain browsers can block information from other programs to come through your email and load properly.
QuickBooks Online (QBO) can also send the email into your customer's spam folders if they aren't able to find it.
If your client is still having issues, I suggest contacting our Customer Support Team. They have more advanced tools to help locate the source of the problem and get it fixed as soon as possible.
Go to the Help icon in the top right-hand corner.
Type in your question to the QB Assistant.
In the end, you can still request a callback from a QBO Specialist by typing that in the QB Assistant. You can also check out our tutorials page for more videos about how to help your business in the future.
It's my priority that your customer is able to open their invoice to pay you. Let me know how it goes. I want to make sure that you're able to get back to running your business. Take care!