Open the hamburger menu of the Nuki App and select Help at the bottom of the list:
Scroll down to the Error log section and make sure Debug mode is enabled.
Open the hamburger menu of the Nuki App again and
- select Manage my devices
- select Smart Lock or Opener
- select an existing device
- click on Manage Opener or Manage Smart Lock
- click on the headline for 7 times to enable/disable debug mode on the device
With debug mode enabled, certain messages are written to the protocol of the device.