ℹ
info Logitech
Status LED flashes blue
Headset has entered Bluetooth pairing mode.
? What Causes This
Power button and Mute button pressed for 3+ seconds.
ⓘ What This Means
Connect to your preferred Bluetooth device.
Source: page 4 of the official manual
From the manual
This error code appears in:
Logitech G435 Wireless Gaming Headset