When I do a routine apt update and apt upgrade running ubuntu, I get two error messages:
An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://cloud.r-project.org/bin/linux/ubuntu bionic-cran35/ InRelease: The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 Michael Rutter firstname.lastname@example.org
W: Failed to fetch https://cloud.r-project.org/bin/linux/ubuntu/bionic-cran35/InRelease The following signatures were invalid: EXPKEYSIG 51716619E084DAB9 Michael Rutter email@example.com
Any suggestions on how to eliminate the message? "InRelease" is a PGP signature. I have removed large parts of R and I'm willing to delete R and re-install it.