Getting Error while upgrading MongoDB

As discussed I’m attempting to update MongoDB from version 3.6 to version 4.0 on Ubuntu 18.0 I’m receiving the error below when updating.

W: GPG error: https://repo.mongodb.org/apt/ubuntu bionic/mongodb-org/4.0 Release: The following signatures were invalid: EXPKEYSIG 68818C72E52529D4 MongoDB 4.0 Release Signing Key <[packaging@mongodb.com](mailto:packaging@mongodb.com)>

E: The repository 'https://repo.mongodb.org/apt/ubuntu 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.

N: See apt-secure(8) manpage for repository creation and user configuration details.