Under these circumstances, the user has to configure the proxy from the deploy.config file, which is normally located in the root of your Qlik Web Connectors folder.
Disabling the proxy:
This is the best approach for Error 503 Service Unavailable errors.
Open the deploy.config file, search for Proxy in order to locate the settings and configure them as below.
How to setup proxy for google cloud storage bucket while connecting through Qlik's GCS bucket connector? Currently, internet access is disabled in the servers and hence cannot access the GCS bucket and don't want to set up the proxy at the servers level and restrict it to only Qlik connectors.