Teamcity Cloud with local build agent: Error while asking server for the communication protocols

I have a TeamCity Cloud beta instance that runs builds with the default cloud agents normally. I want to add a local build agent but I continue getting the following error: Error while asking server for the communication protocols.

I downloaded the config file from the web interface and the agent shows in my list of agents but never connects. Is this even supposed to work with TeamCity Cloud? I'm at a basic home network with nothing blocked. I have defined JAVA_HOME=/usr/lib/jvm/default-java/bin

My java version is: java -version
openjdk version "10.0.1" 2018-04-17
OpenJDK Runtime Environment (build 10.0.1+10-Ubuntu-3ubuntu1)
OpenJDK 64-Bit Server VM (build 10.0.1+10-Ubuntu-3ubuntu1, mixed mode)

Any help would be appreciated!