Note that the XML-RPC API is a legacy API and is no longer being developed, we recommend using the REST API instead.
The XML-RPC API uses IP addresses for access control. If you encounter error messages like this:
IP address not authorized for 351161: 127.0.0.1
you need to add this IP address to the list of allowed addresses. This can be done in the Console under Settings > API. (Requires Administrator privileges.)