$ sudo apt update
Hit:1 Index of /debian/ stretch InRelease
Ign:2 Index of /debian stretch InRelease
Get:3 http://security.debian.org stretch/updates InRelease [53.0 kB]
Get:4 Index of /debian stretch-updates InRelease [93.6 kB]
Hit:5 Index of /debian stretch Release
Err:6 Index of /php/ stretch InRelease
The following signatures were invalid: EXPKEYSIG B188E2B695BD4743 DEB.SURY.ORG Automatic Signing Key deb@sury.org
Fetched 147 kB in 0s (268 kB/s)
Reading package lists… Done
Building dependency tree
Reading state information… Done
35 packages can be upgraded. Run ‘apt list --upgradable’ to see them.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: Index of /php/ stretch InRelease: The following signatures were invalid: EXPKEYSIG B188E2B695BD4743 DEB.SURY.ORG Automatic Signing Key deb@sury.org
W: Failed to fetch https://packages.sury.org/php/dists/stretch/InRelease The following signatures were invalid: EXPKEYSIG B188E2B695BD4743 DEB.SURY.ORG Automatic Signing Key deb@sury.org
W: Some index files failed to download. They have been ignored, or old ones used instead.