<?php

$curl = curl_init();

curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://api.ysltsender.com/v1/otp/send',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => '',
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 0,
  CURLOPT_FOLLOWLOCATION => true,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => 'POST',
  CURLOPT_POSTFIELDS =>'{
  "phone": "+1234567890",
  "channel": "sms",
  "length": 6,
  "expires_in": 300
}',
  CURLOPT_HTTPHEADER => array(
    'Content-Type: application/json',
    'Accept: application/json',
    'Authorization: Bearer <api_key>'
  ),
));

$response = curl_exec($curl);
curl_close($curl);
echo $response;