When using yarn through the apt repo, the key might expire, giving you the following error when updating apt.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://dl.yarnpkg.com/debian stable InRelease: The following signatures were invalid: EXPKEYSIG 23E7166788B63E1E Yarn Packaging <yarn@dan.cx>
W: Failed to fetch https://dl.yarnpkg.com/debian/dists/stable/InRelease The following signatures were invalid: EXPKEYSIG 23E7166788B63E1E Yarn Packaging <yarn@dan.cx>
W: Some index files failed to download. They have been ignored, or old ones used instead.
Issue the following command to update the key and then update the repository.
curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -