Update

//  Create a Map to store all the data of a Contact
Map<String, Object> contactMap = new Map<String, Object>(); 
    contactMap.put('ContactID', '950f2525-14a8-4871-8348-980d6b9c5757');
	contactMap.put('Name', 'Breadwinner Inc');
	contactMap.put('SkypeUserName', 'jack.Rogers');

//  Initializing the RequestJSON Data to be passed.
Map<String, Object> requestJSONMap = new Map<String, Object>();
    requestJSONMap.put('contacts', new List<Object>{contactMap});
    String reqJSON = JSON.serialize(requestJSONMap);

Map<String, Object> reqObj = new Map<String, Object>();
    reqObj.put('version', '1.0');
    reqObj.put('action', 'updateContact');
    reqObj.put('requestJSON', reqJSON);
    //Required, if Xero Multi-Org is enabled in Breadwinner. 
    reqObj.put('xeroOrgId', '!aa00TM');  
    
//  Placing a request to Breadwinner Global API
Map<String, Object> respMap = bread_winner.BreadwinnerXeroAPI.call(reqObj);
System.debug(respMap);