This is because there are different Statuses for an Event Registration.

Navigate to:
  1. onMessage > Approval > Event Registration
  2. Click Edit into the Registration in question
  3. Click Registries
  4. Select the dropdown for Status such as Not Handled, Handled, All, Payment Processed, and Payment Not Processed (you can also mark the show Failed checkbox if you are having issues with users that got an error or had an issue with Payment)
  5. Click View