pre-built extra dependencies

Hello! According to build instructions in https://mirror.git.trinitydesktop.org/gitea/TDE/tde-packaging/src/branch/ma… (the item 9.1 there) I tried to do the following steps: *) apt-key adv --keyserver pool.sks-keyservers.net --recv-key A04BE668 *) added "deb http://mirror.ppa.trinitydesktop.org/trinity-sb stretch deps-r14" into /etc/apt/sources.list *) apt update The "apt-key" command printed this and finished successfully: Warning: apt-key output should not be parsed (stdout is not a terminal) Executing: /tmp/apt-key-gpghome.XvV2j9eAug/gpg.1.sh --keyserver pool.sks-keyservers.net --recv-key A04BE668 gpg: key 608F5293A04BE668: 7 signatures not checked due to missing keys gpg: key 608F5293A04BE668: public key "Slvek Banko <slavek.banko(a)axis.cz>" imported gpg: Total number processed: 1 gpg: imported: 1 But the "apt update" failed with the following message: Get:6 http://mirror.ppa.trinitydesktop.org/trinity-sb stretch InRelease [40.8 kB] Err:6 http://mirror.ppa.trinitydesktop.org/trinity-sb stretch InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C93AF1698685AD8B Reading package lists... W: GPG error: http://mirror.ppa.trinitydesktop.org/trinity-sb stretch InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY C93AF1698685AD8B E: The repository 'http://mirror.ppa.trinitydesktop.org/trinity-sb stretch InRelease' is not signed. My question is if I misunderstood the instructions somehow and if not, how to continue from there? Cheers, Ilya D.