php - Curl:Unknown SSL protocol error gcm -

enter image description herei have designed gcm server in php(mamp). curl version-7.43.0,php version 7.0.0 .the code server-

<?php    function send_push_notification($registration_id,$message){     define('api_key','aizasyaofih8qeflois3vvwhsxxllxxxxxxxxxx');     $url='https://gcm-http.googleapis.com/gcm/send';      $fields=array(         'registration_id'=>$registration_id,         'data'=>$message,         );     $headers=array(         'authorization:key='.api_key,         'content-type:application/json'         );      $ch=curl_init();     curl_setopt($ch, curlopt_url, $url);     curl_setopt($ch, curlopt_post, true);     curl_setopt($ch, curlopt_post, true);         curl_setopt($ch, curlopt_httpheader, $headers);         curl_setopt($ch, curlopt_returntransfer, true);           curl_setopt($ch, curlopt_ssl_verifypeer, false);          curl_setopt($ch, curlopt_postfields, json_encode($fields));          curl_setopt($ch, curlopt_ssl_verifypeer, 0);         curl_setopt($ch, curlopt_sslversion, 3);      $result = curl_exec($ch);         if ($result === false) {             die('curl failed: ' . curl_error($ch));         }          // close connection         curl_close($ch);         echo $result;  }    ?> <?php send_push_notification("e2dgrszpgku:apa91bf_73a6-o5clv-gdczzyfabtikjqi-5w6gdscara4z8-1iglev5ss6hqkw8pj_g_dxbe7jldsopmgu3y1gkkw1vpn_zewiecwbsitpd0plwaz50w8uzhknghvnf1xxxxxxxxxxx","hi"); ?> 

when try running php script in browser shows following error

curl failed: unknown ssl protocol error in connection gcm-http.googleapis.com:443

i have disabled ssl verification,still shows curl error.

changing ssl version 6 worked me.

curl_setopt($ch,curlopt_sslversion,6);