// Create a Map to store all the data of a Purchase Order
Map<String, Object> nsPurchaseorder = new Map<String, Object>();
nsPurchaseorder.put('classification', new Map<String, Object>{'internalId'=>'5'});
nsPurchaseorder.put('currencyRecord', new Map<String, Object>{'internalId'=>'1'});
nsPurchaseorder.put('department', new Map<String, Object>{'internalId'=>'2'});
nsPurchaseorder.put('dueDate', DateTime.newInstance(2020, 12, 31).getTime()/1000);
nsPurchaseorder.put('entity', new Map<String, Object>{'internalId'=>'30440'});
nsPurchaseorder.put('shipTo', new Map<String, Object>{'internalId'=>'362'});
nsPurchaseorder.put('memo', 'PO 12');
nsPurchaseorder.put('otherRefNum', '4343399');
nsPurchaseorder.put('tranDate', DateTime.newInstance(2020, 09, 07).getTime()/1000);
// Initializing the Purchase Order Custom Fields
List<Object> poCustomFieldList = new List<Object>();
Map<String, Object> poCustomField = new Map<String, Object>();
poCustomField.put('fieldType', 'select');
poCustomField.put('scriptId', 'custbody_customlist');
poCustomField.put('valueLookup', new Map<String, Object>{'internalId'=>'2'});
poCustomFieldList.add(poCustomField);
// Adding the Purchase Order Custom Fields
nsPurchaseorder.put('customFieldList', new Map<String, Object>{'customField'=>poCustomFieldList});
// Initializing the Purchase Order Line Items
List<Object> lineItemList = new List<Object>();
Map<String, Object> lineItem = new Map<String, Object>();
lineItem.put('description', 'A weapon for shooting arrows');
lineItem.put('item', new Map<String, Object>{'internalId'=>'239'});
lineItem.put('quantity', 1);
lineItem.put('rate', '999');
// Initializing the Line Item custom fields
List<Object> liCustomFieldList = new List<Object>();
Map<String, Object> liCustomField = new Map<String, Object>();
liCustomField.put('fieldType', 'boolean');
liCustomField.put('scriptId', 'custcol_checkbox');
liCustomField.put('value', 'true');
liCustomFieldList.add(liCustomField);
// Adding the Purchase Order Line Item Custom Fields
lineItem.put('customFieldList', new Map<String, Object>{'customField'=>liCustomFieldList});
lineItemList.add(lineItem);
// Adding the Line Items to Purchase Order
Map<String, Object> poLineitemList = new Map<String, Object>();
poLineitemList.put('item', lineItemList);
nsPurchaseorder.put('itemList', poLineitemList);
// Initializing the RequestJSON Data to be passed.
Map<String, Object> requestJSONMap = new Map<String, Object>();
requestJSONMap.put('purchaseOrders', new List<Object>{nsPurchaseorder});
String reqJSON = JSON.serialize(requestJSONMap);
Map<String, Object> reqObj = new Map<String, Object>();
reqObj.put('version', '1.0');
reqObj.put('action', 'createPurchaseOrder');
reqObj.put('requestJSON', reqJSON);
// Placing a request to Breadwinner Global API
Map<String, Object> resp = breadwinner_ns.BreadwinnerNetSuiteAPI.call(reqObj);
System.debug(resp);