Can't install metrics

I am trying to follow the instructions here https://www.digitalocean.com/docs/monitoring/how-to/upgrade-legacy-agent/ to “Update Droplet to Monitoring”.

sudo apt-get purge do-agent
curl -sSL https://repos.insights.digitalocean.com/install.sh | sudo bash

My droplet is using “Ubuntu MEAN on 14.04”

I am getting the following output

> sudo apt-get purge do-agent

Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package do-agent

> curl -sSL https://repos.insights.digitalocean.com/install.sh | sudo bash

Cleaning up old sources...OK
Verifying machine compatability...OK
Verifying compatability with script...OK
Installing apt repository...
Splitting up /var/lib/apt/lists/partial/downloads-distro.mongodb.org_repo_ubuntu-upstart_dists_dist_InRelease into data and signature failedE: GPG error: http://downloads-distro.mongodb.org dist InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?)
E: Unable to correct problems, you have held broken packages.

I tried running sudo apt-get update but it still can’t find the do-agent package. Any idea what could be causing these errors?