Is it correct to pass XML using cURL php?

Question

PHP

I form xml and pass it as a parameter to the function that sends a POST request using cURL, and when I display a variable with my XML in the function that should send the request, I get the line there:

string(793) " CampaignId EQUALS 191853 Date Clicks Cost AdNetworkType Date Campaign #191853, August CUSTOM_REPORT THIS_MONTH TSV NO NO "

This is fine? Is this string transmitted by cUrl or is it xml?
Function forming xml:

function custom_report(  ) {
  $service = "reports";

  $data ='<?xml version="1.0" encoding="UTF-8"?>
    <ReportDefinition xmlns="https://api.direct.yandex.com/v5/reports">
    	<SelectionCriteria>
    		<Filter>
    			<Field>CampaignId</Field>
    			<Operator>EQUALS</Operator>
    			<Values>191853</Values>
    		</Filter>
    	</SelectionCriteria>
    	<FieldNames>Date</FieldNames>
    	<FieldNames>Clicks</FieldNames>
    	<FieldNames>Cost</FieldNames>
    	<FieldNames>AdNetworkType</FieldNames>
    	<OrderBy>
    		<Field>Date</Field>
    	</OrderBy>
    	<ReportName>Campaign #191853, August</ReportName>
    	<ReportType>CUSTOM_REPORT</ReportType>
    	<DateRangeType>THIS_MONTH</DateRangeType>
    	<Format>TSV</Format>
    	<IncludeVAT>NO</IncludeVAT>
    	<IncludeDiscount>NO</IncludeDiscount>
    </ReportDefinition>';
   
return QueryToYandex( $service, $data );
}

Sending a request:

function QueryToYandex( $service, $data ) {

        var_dump($data);  //здесь получаю строку

  $tokenYandex = "";

  $curl = curl_init();

  curl_setopt_array($curl, array(
    CURLOPT_URL => "https://api-sandbox.direct.yandex.com/v5/".$service,
    CURLOPT_RETURNTRANSFER => true,
    CURLOPT_POST => true,
    CURLOPT_PROTOCOLS => CURLPROTO_HTTPS,
    CURLOPT_TIMEOUT => 30,
    CURLOPT_CUSTOMREQUEST => "POST",
    CURLOPT_HTTPHEADER => array(
      "accept-language: ru",
      "authorization: Bearer ".$tokenYandex,
      "Client-Login: asdsad",
      "processingMode: online",
      "returnMoneyInMicros: false"
      ),
    )
  );
        curl_setopt($curl, CURLOPT_POSTFIELDS, $data);
  $res = curl_exec($curl);

  if(!$res){
    $error = curl_error($curl).'('.curl_errno($curl).')';
    $res = $error;
  }
  else
    curl_close($curl);
  
  return $res;
}

Answer 1

This line is your XML, it just looks like you're outputting it to the browser.
Try outputting to textarea, or open source and see.