Create

// Create a Map to store all the data of a Invoice
List<Object> invoiceList = new List<Object>();
Map<String, Object> invoiceMap = new Map<String, Object>();
   invoiceMap.put('Type', 'ACCREC');
   invoiceMap.put('DateString', '2021-11-11T00:00:00');
   invoiceMap.put('DueDateString', '2021-12-06T00:00:00');
   invoiceMap.put('LineAmountTypes', 'Exclusive');
   invoiceMap.put('Status', 'DRAFT');

// Initializing the Contact
Map<String, Object> contactMap = new Map<String, Object>();
   contactMap.put('ContactID', 'c84ebb15-0a8d-4145-933f-203e68d014a0');
   invoiceMap.put('Contact', contactMap);

// Initializing the Invoice Line Items
List<Object> lineItemList = new List<Object>();
Map<String, Object> lineItemMap = new Map<String, Object>(); 
   lineItemMap.put('Description', 'Line Item Description');
   lineItemMap.put('UnitAmount', 100);
   lineItemMap.put('Quantity', 10);
   lineItemMap.put('AccountCode', '200');
   lineItemList.add(lineItemMap);

// Adding the Line Items to Invoice
   invoiceMap.put('LineItems', lineItemList);
   invoiceList.add(invoiceMap);

// Initializing the RequestJSON Data to be passed.
Map<String, Object> reqJSONMap = new Map<String, Object>(); 
   reqJSONMap.put('invoices', invoiceList); 
   String reqJSON = JSON.serialize(reqJSONMap); 

Map<String, Object> finalReqMap = new Map<String, Object>(); 
Map<String, Object> reqOptions = new Map<String, Object>(); 
   finalReqMap.put('queryParameters', reqOptions); 
   finalReqMap.put('version', '1.0'); 
   finalReqMap.put('action', 'createInvoice'); 
   finalReqMap.put('RequestJSON', reqJSON); 
   finalReqMap.put('skipDML', false); 
   //Required, if Xero Multi-Org is enabled in Breadwinner. 
   finalReqMap.put('xeroOrgId', '!aa00TM');
   System.debug('Request ::: ' + finalReqMap);

// Placing a request to Breadwinner Global API
Map<String, Object> respMap = bread_winner.breadwinnerXeroAPI.call(finalReqMap);
System.debug('Response ::: ' + respMap);