If you've receiving error occurred while playing back on iOS, try resetting the date and time on your device.
Step 1: Go to settings on your iOS device.
Step 2: Turn off the set automatically by tapping the toggle button available at the right side of the option.
Step 3: Manually configure the Date & Time
Step 4: Set the time zone appropriately.
Step 5: Toggle back to set automatically and close out and reopen the Napster App and try to playback the tracks again.
If you are still seeing the error afterwards please email firstname.lastname@example.org with the following information.