Authentication failure on Linux

I’m getting:

“There were unauthenticated packages and -y was used without --allow-unauthenticated”

The problem seems to be related to

[0K$ sudo -E apt-add-repository -y "ppa:ubuntu-toolchain-r/test"
gpg: keyring `/tmp/tmp6a2v61ol/secring.gpg' created
gpg: keyring `/tmp/tmp6a2v61ol/pubring.gpg' created
gpg: requesting key BA9EF27F from hkp server
gpgkeys: key 60C317803A41BA51845E371A1E9377A2BA9EF27F can't be retrieved
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0