var client = new RestClient("https://nibrs.ariesportal.com/NIBRS-Upload/api/XMLUpload");
var request = new RestRequest(Method.POST);
request.AddHeader("Cache-Control", "no-cache");
request.AddHeader("Content-Type", "application/xml");
request.AddHeader("Authorization", "Basic WW91ck9SSTpZb3VyUGFzc3dvcmQ=");
request.AddParameter("application/xml", "<UploadContainer xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\">\r\n<Files>\r\n<NibrsXmlUpload>\r\n<FileName>Test</FileName>\r\n<XML><REPLACE WITH BASE 64 ENCODED STRING OF XML DATA></XML>\r\n</NibrsXmlUpload>\r\n<NibrsXmlUpload>\r\n<FileName>Test2</FileName>\r\n<XML><REPLACE WITH BASE 64 ENCODED STRING OF XML DATA></XML>\r\n</NibrsXmlUpload>\r\n</Files>\r\n</UploadContainer>", ParameterType.RequestBody);
IRestResponse response = client.Execute(request);
            

<?php

$request = new HttpRequest();
$request->setUrl('https://nibrs.ariesportal.com/NIBRS-Upload/api/XMLUpload');
$request->setMethod(HTTP_METH_POST);

$request->setHeaders(array(
  'Postman-Token' => '16d6263f-a1f7-4019-b489-98737623b6eb',
  'Cache-Control' => 'no-cache',
  'Content-Type' => 'application/xml',
  'Authorization' => 'Basic WW91ck9SSTpZb3VyUGFzc3dvcmQ='
));

$request->setBody('<UploadContainer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Files>
        <NibrsXmlUpload>
            <FileName>Test</FileName>
            <XML><REPLACE WITH BASE 64 ENCODED STRING OF XML DATA></XML>
        </NibrsXmlUpload>
        <NibrsXmlUpload>
            <FileName>Test2</FileName>
            <XML><REPLACE WITH BASE 64 ENCODED STRING OF XML DATA></XML>
        </NibrsXmlUpload>
    </Files>
</UploadContainer>');

try {
  $response = $request->send();

  echo $response->getBody();
} catch (HttpException $ex) {
  echo $ex;
}
            

curl --request POST \
  --url https://nibrs.ariesportal.com/NIBRS-Upload/api/XMLUpload \
  --header 'Authorization: Basic WW91ck9SSTpZb3VyUGFzc3dvcmQ=' \
  --header 'Cache-Control: no-cache' \
  --header 'Content-Type: application/xml' \
  --data '<UploadContainer xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">\r\n    <Files>\r\n        <NibrsXmlUpload>\r\n            <FileName>Test</FileName>\r\n            <XML><REPLACE WITH BASE 64 ENCODED STRING OF XML DATA></XML>\r\n        </NibrsXmlUpload>\r\n        <NibrsXmlUpload>\r\n            <FileName>Test2</FileName>\r\n            <XML><REPLACE WITH BASE 64 ENCODED STRING OF XML DATA></XML>\r\n        </NibrsXmlUpload>\r\n    </Files>\r\n</UploadContainer>'