GPG couldn't be verified

[LiohMoeller]

Err:1 https://artifacts.chirpstack.io/packages/3.x/deb stable InRelease
  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY CFF064C9D12ECB34
Reading package lists... Done
W: GPG error: https://artifacts.chirpstack.io/packages/3.x/deb stable InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY CFF064C9D12ECB34
E: The repository 'https://artifacts.chirpstack.io/packages/3.x/deb stable InRelease' is not signed.

Key is not available on any know keyservers nor within the Repository. Please publish the GPG Public Key on the Repository and optionally on keyservers.