Will need more information so I can better understand the problem.
@"clark8888" @"jetski" when you can, please run the following via SSH:
sudo systemctl stop snakeoil-rest
QT_PLUGIN_PATH=/usr/local/lib/plugins/ snakeoil-rest --verbosity 10
If everything works, you should see this:
[5] Snakeoil API Listening to requests at: 127.0.0.1:30511 [helper/rest_server.cpp:58|rest_server_c::listen()]
Wait about 30 seconds and see if it crashes, and then go to the WebApp and see if it's working. You wouldn't see a 503 error if you see the above line.