I suspect this is for LoRa and in Chirpstack.
Firstly there are two methods to add sensors in LoRa. Either OTAA (over the air activation) or ABP (Activation By Personalization). Most sensors and users will probably use OTAA. This is set by using the correct device profile. In the IoT Open standard server they are usually named something with either OTAA or ABP.
When an OTAA profile is selected Chirpstack should show "Application Key" under the "Keys (OTAA)" tab. Input the provided encryption key here and press save.
