java - Use Backendless behind proxy

Question

I'm trying to use Backendless framework in my Java server but I'm working behind a corporative http proxy and I get UnknownHostException when I do things like:

Backendless.Persistence.save(employee);

I have tried to put http.proxyHost and http.proxyPort JVM options but I still get the same error. I have tried with java.net.useSystemProxies, too.

Thanks in advance.