The plugin provides two approaches to debugging.
One is to use the show_xml= parameter, setting it to "y" or "yes". This displays the XML request and response instead of what appears between the eemindbody opening and closing tags. The show_xml="y" option should help if you are receiving data but it isn't quite what you expect, or for a quick peek/reminder of the data fields available.
The second approach is to use EE's template debugging log. If there are any errors then the plugin displays the text "eemindbody" in bold followed by an explanation. If the call to MindBody failed, due to say a credentials or network error, then these SoapFault and Exception errors are displayed with accompanying messages. If the call to MindBody succeeds but the data returned is bad, ie, if the SOAP Response field "Status" does not have a value of "Success", then the Status and accompanying message is displayed.