Update

//  Create a Map to store all the data of a Customer
Map<String, Object> paymentMap = new Map<String, Object>(); 
    paymentMap.put('Id','889');
    paymentMap.put('TotalAmt','200');
    paymentMap.put('CustomerRef' , new Map<String, Object>{'value' => '226'});
	paymentMap.put('SyncToken','0');
	paymentMap.put('PrivateNote','Memo field updated');

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

Map<String, Object> reqObj = new Map<String, Object>();
    reqObj.put('version', '1.0');
    reqObj.put('action', 'updatePayment');
    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);