HttpRequest req = new HttpRequest();
req.setMethod('POST');

req.setEndpoint('https://ZXXXXXXXX/api/ZXXXXXXXX');
String username = 'ZXXXXXXXX';
String password = 'XXXXXXXXXXXXXXX';
Blob headerValue = Blob.valueOf(username + ':' + password);
String authorizationHeader = 'Basic ' +
EncodingUtil.base64Encode(headerValue);
req.setHeader('Authorization', authorizationHeader);
req.setHeader('Content-Type', 'application/json');

req.setBody(JSON.serialize(lstOfObjectIWantToSend));


System.debug('json serialized object:
'+JSON.serialize(lstOfObjectIWantToSend));

HttpResponse res = new Http().send(req);

System.debug('Response from Server in Salesforce: '+res);