API WordPress is Limited? Return False

If you are not getting anything meaningful from API responses I would recommend to enable WP_DEBUG and logging server–side. Though in many cases WP doesn’t handles error silently, so you might need to add and log some checks of your own to source.

As a more general advice XMLRPC is sort of dusty. New REST API is being developed and (slowly) added to core, you could try with that one.