confirmation of TDE key ring failure

Hello ! For several days now, I get the following error when updating or upgrading my TDE.  Note: I am using the development archive for debian/buster or debian/stretch testing; i.e., deb http://mirror.ppa.trinitydesktop.org/trinity-sb buster deps-r14 main-r14 (or buster if testing buster). The error messages from stretch update: 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 W: The repository 'http://mirror.ppa.trinitydesktop.org/trinity-sb stretch InRelease' is not signed. N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use. N: See apt-secure(8) manpage for repository creation and user configuration details. A similar error message if updating the buster archive. Yes, I have installed ii  trinity-keyring  4:14.0.7~pre3-0debian9.0.0+2 all  GnuPG key of the Trinity Desktop Environment repository and, I have also tried the command wget http://mirror.ppa.trinitydesktop.org/trinity/deb/trinity-keyring.deb but cannot seem to rid the error. The testing is going fine and I can actually install the packages with the "--allow-unauthenticated", but of course, I would rather not ! Anyone else with this problem?  Is there a way to correct it on my end? -- James D. Freels, Ph.D., P.E. freelsjd(a)gmail.com