QB Issue Resolution:

Select the blue navigation bar on the left

Select Customers Center
Locate Customer and click “Open Invoices” under Pending Invoices column
Under “Status” column you will notice either “Open (Viewed)” or Open (Sent).”
That’s your confirmation if the invoice has been viewed or not.

Resolution for Issue 'Can I see if my customer opened my sender invoice? how?' available: Yes (Solved).
Source: Intuit Community forum.

Can I see if my customer opened my sender invoice? how?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for Customer
Quickbooks Repair Pro will resolve it efficiently and affordably. Guaranteed resolution of your issue, or you pay nothing!

Error Recovery for Customer [Canada]
E-Tech is the #1 Quickbooks data migration and Conversion service provider.

Get 50% off Quickbooks Online

Click Here for 50% off!

Additional Support Options: