If you get the error message “Failed to send pair request” when using “ltunify pair” it may be due to that the number of devices you have paired has reached the maximum number.

Check this by typing

ltunify list

If you have 6 paired devices (at least on my computer running Arch) you will get the error message. You may find the maximum number by typing “ltunify”.

Just unpair one of the devices you are not using

ltunify unpair idx

Where idx is the number of the device to be unpaired.

Then try pairing your device again.