/Coveo/Rest returns 503 Service not available
I have a multi server Sitecore install. Coveo is installed on CA server.
From one of the CD servers I can't access to http:[CDServerURL]/coveo/rest - I get 503 : The service is unavailable
I can access to CA server admin service and CoveoSearchService fine from the problematic "CD" server.
I checked Rest.Config and verified I am pointing to the right server and port number. This works for other CD servers so I assume config.YML is fine ( allowimpersonate etc.. )
Does the application secret specified in Coveo.SearchProvider.Rest.config matches with the one in config.yml?