This is a common error when you install MongoDB due to failed key verification.
To fix this run the following command:
/usr/bin/curl -sLO https://www.mongodb.org/static/pgp/server-4.4.asc && sudo /usr/bin/apt-key add server-4.4.asc
The 4.4 in the command above refers to the database version. You may change it to the version you are actually installing.
sudo apt-get update
Now you may install MongoDB by running:
sudo apt-get install -y mongodb-org
Start the MongoDB once it is installed:
sudo systemctl start mongod
Check if its running using this command:
sudo systemctl status mongod