[ This is just to share if you are facing same issue. ]
Solved the following invalid signatures error by executing "sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B7B3B788A8D3785C"
**Error: **
#apt update
Get:1 http://repo.mysql.com/apt/ubuntu jammy InRelease [30.0 kB]
Hit:2 http://mirrors.linode.com/ubuntu jammy InRelease
Hit:3 http://mirrors.linode.com/ubuntu jammy-updates InRelease
Hit:4 http://mirrors.linode.com/ubuntu jammy-backports InRelease
Hit:5 https://download.docker.com/linux/ubuntu jammy InRelease
Err:1 http://repo.mysql.com/apt/ubuntu jammy InRelease
The following signatures were invalid: EXPKEYSIG B7B3B788A8D3785C MySQL Release Engineering mysql-build@oss.oracle.com
.
.
34 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: http://repo.mysql.com/apt/ubuntu jammy InRelease: The following signatures were invalid: EXPKEYSIG B7B3B788A8D3785C MySQL Release Engineering mysql-build@oss.oracle.com
W: Failed to fetch http://repo.mysql.com/apt/ubuntu/dists/jammy/InRelease The following signatures were invalid: EXPKEYSIG B7B3B788A8D3785C MySQL Release Engineering mysql-build@oss.oracle.com
W: Some index files failed to download. They have been ignored, or old ones used instead.
#sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys B7B3B788A8D3785C
