W: GPG error: MongoDB Repositories bionic/mongodb-org/4.0 Release: The following signatures were invalid: EXPKEYSIG 68818C72E52529D4 MongoDB 4.0 Release Signing Key packaging@mongodb.com
E: The repository ‘MongoDB Repositories bionic/mongodb-org/4.0 Release’ is not signed.
N: Updating from such a repository can’t be done securely, and is therefore disabled by default.
As we need to upgrade from 3.6 to 5.0 in ubuntu 18