Critical - P2 On https://docs.mongodb.com/manual/tutorial/install-mongodb-on-debian/ for 3.6 on the seconds step (Create a /etc/apt/sources.list.d/mongodb-org-3.6.list file for MongoDB), command for debian 9 is using placeholders instead of 3.6 version
echo "deb http://repo.mongodb.org/apt/debian stretch/mongodb-org/{+package-branch+} main" | sudo tee /etc/apt/sources.list.d/mongodb-org-{+version+}.list
should be
echo "deb http://repo.mongodb.org/apt/debian stretch/mongodb-org/3.6 main" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.6.list
