Read

//  Create a Map to store all the data of a Invoice
Map<String, Object> invoiceMap = new Map<String, Object>();
invoiceMap.put('Id','13');

//  Initializing the Request Data to be passed.
    Map<String, Object> reqObj = new Map<String, Object>();
    reqObj.put('version', '1.0');
    reqObj.put('action', 'readInvoice');
    reqObj.put('options',invoiceMap);
    //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);