On enrolling the .deb 7.11-SNAPSHOT package agent, we are getting the following message
"Usage: /etc/init.d/elastic-agent {start|stop|status|restart|force-reload}"
and are unable to enroll the .deb agent using the following steps on Linux Debian 9 with .deb or a Centos8 with .rpm instance (verified on both, but deb example is given below:

Steps followed:

Download the "elastic-agent-7.11.0-amd64.deb" package artifact page.
Agent: https://snapshots.elastic.co/7.11.0-2a00e604/downloads/beats/elastic-agent/elastic-agent-7.11.0-SNAPSHOT-amd64.deb

place the agent package on home/zeus location on Debian 9 Linux machine.

Run the command to get the root/admin permission: sudo su root

sudo dpkg -i elastic-agent-7.11.0-SNAPSHOT-amd64.deb

sudo elastic-agent enroll https://df36b1e2a07749b8842cecf42ae7358a.us-central1.gcp.foundit.no:9243 SG5ZdS1IVUI2UFEzTEg4aEgyWGI6VEUzbnB6QjRRYWF0aW1Bbkg5XzBCUQ==

Observe "Usage: /etc/init.d/elastic-agent {start|stop|status|restart|force-reload}" message is displayed.

Execute sudo /etc/init.d/elastic-agent start
and observe that .deb agent is not displayed in UI.

screenshot