For Rackspace Monitoring, use the following endpoint to access the API. Replace the $TENANT_ID variable with your Rackspace Cloud account number which is available from the Cloud Control Panel.
https://monitoring.api.rackspacecloud.com/v1.0/$TENANT_ID
You can find the complete URI to access the Rackspace Monitoring API in the service catalog that is returned in the authentication response. Search the catalog for the service name, rax:monitor . Then copy the URI from the publicURL field included in the service information.