From there, you'll see if the customer has viewed it or not yet after sending the invoice. From the Sales tab, select Invoices and locate invoice. Under the Status column, you'll see if your client viewed it inside the parenthesis. You can also click on the arrow down and you'll see that the Viewed status has check on it.
Also, you can open the invoice and go to the Activities section at the bottom. From there, you can see when exactly the customer open and viewed it.
My Quickbooks doesn’t indicate when customer has viewed invoice
You can see if an invoice has been viewed by accessing QuickBooks through a web browser. You mentioned whenever you try to verify whether an invoice has been seen in the desktop and Android apps, it doesn't display this information. I did some research into this for you, and am not finding that our desktop or mobile app support this feature yet. This feature is only available in the browser at this time. I can submit feedback to our product development team for you so this is considered for future updates.
If you sign in through a web browser, you'll be able to follow the same steps that @AlexV provided and see if an invoice has been viewed or not. However, there are other factors involved with this too. QuickBooks Online has multiple options for delivering invoices to your customers. It will only track if it was viewed if you have it set to Online Invoice.
Here's how to make sure it's setup properly:
1. Go to the Gear icon, then Account and Settings.
2. Click to the Sales tab.
3. Find the Online Delivery section and open the Additional Email Options drop-down menu, then select the option for Online Invoice.
4. Save your preferences.
After completing those steps, any invoices you send out will be tracked through QuickBooks, and their statuses will be visible when accessing through a web browser.
If you still need assistance with this, just let me know and I'll be here to help.