Debian reposity pubkey not found

[Petr Boltík]

Hi, please check pubkey for your debian repository. No valid pubkey found.
Regards Petr

Debian 10.3
installation from https://bird.network.cz/?download&tdir=debian/

apt-key add - ..... OK
~# apt update
Err:2 http://bird.network.cz/debian buster InRelease
  The following signatures couldn't be verified because the public key is
not available: NO_PUBKEY B188E2B695BD4743
Reading package lists... Done
W: GPG error: http://bird.network.cz/debian buster InRelease: The following
signatures couldn't be verified because the public key is not available:
NO_PUBKEY B188E2B695BD4743
E: The repository 'http://bird.network.cz/debian buster InRelease' is not
signed.
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