Check whether the master config-sources.yml file exists and it is a valid YAML file.

Check whether the locations of the configuration files are correctly configured in the master configuration file.

Check whether the configuration files are valid YAML files.

Check whether the configuration files contain the right structure and names for the settings as provided in the templates.

Check whether the configured external instance (Elasticsearch or Kibana) is running before starting API Gateway.

Check for the logs by enabling debug level of the Externalized Configuration facility in the logging settings.