Make sure they use the same kind of Bluetooth.
BlueTooth (classic or BT) and the low energy BlueTooth LE (BTLE or BLE) are not compatible. They are both stamped with the same Bluetooth rune symbol, and both have the 'Bluetooth' word in their naming, but they use different data rates, different hopping frequency and different modulation type IIRC. This is not obvious in most laptops and mobile phones, because they can do both standards, but dedicated devices might not be able to work with any Bluetooth.
Just a hunch, I don't know which kind of Bluetooth is used by the Yaesu modules, or by the Bosse headset.
Assuming your devices are using the more recent 'low energy' Bluetooth, the key exchange (for pairing) can be either:
- OOBK (out of band key exchanging) which means the key is exchanges not by radio, but by other means. Either a fixed key, or a key sent by plugging the device into a PC, etc.
- password number 0...999999
- 'JustWorks' mode (in which the password number is always '0')