Update

//  Create a Map to store all the data of a Customer
Map<String, Object> customerMap = new Map<String, Object>(); 
    customerMap.put('DisplayName','Weiskopf Consulting');
	customerMap.put('Id','1201');
	customerMap.put('SyncToken','0');

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

Map<String, Object> reqObj = new Map<String, Object>();
    reqObj.put('version', '1.0');
    reqObj.put('action', 'updateCustomer');
    reqObj.put('requestJSON', reqJSON);
    //Required, if QuickBooks Multi-Org is enabled in Breadwinner. 
    reqObj.put('qbOrgId', '!aa00TM');

//  Placing a request to Breadwinner Global API
Map<String, Object> respMap = breadwinner_qbo.BreadwinnerQBAPI.call(reqObj);
System.debug(respMap);