Invalid json format using this api when using curl php - php

Question

This is my json data
$data = array(
"api_key"=>"xxxx",
"email_details"=> array( "fromname"=>"test",
"subject"=>"Registration",
"from"=>"xxx#xxx.com",
"content"=>"test"),
"recipients"=>["xxx#gmail.com"]
);
generated the json data:
$str_data = json_encode($data);
it gives following format of json:
{"api_key":"xxxx",
"email_details":{"fromname":"test","subject":"Registration","from":"xxx#xxx.com","content":"test"},
"recipients":["xxx#gmail.com"]}
it is valid json format
verified from this url
http://jsonlint.com/
from the postman i have tried to run the API:
https://api.xxx.com/xxx/json?data={"api_key":"xxxx","email_details": {"fromname":"xxx","subject":"Registration","from":"xxx#xxx.com","content":"test" },"recipients":["xxx#gmail.com"]}
it is given the success message
when i tried to run this api from php code :
$url_email="https://api.xxx.com/xxx/json?data=";
$chh = curl_init();
curl_setopt($chh, CURLOPT_URL,$url_email);
curl_setopt($chh, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($chh, CURLOPT_POSTFIELDS, $str_data);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/json',
'Content-Length: ' . strlen($str_data))
);
curl_setopt($chh, CURLOPT_RETURNTRANSFER, true);
curl_exec($chh);
curl_close($chh);
i didn't get the o/p
getting the error message :
{"message":"ERROR","errorcode": "100" ,"errormessage":"Invalid JSON format used in API Call.Hence failed."}
whats wrong here ?

Answer 1

I suppose it should be:
$url_email="https://api.xxx.com/xxx/json"; // no `data` here
$chh = curl_init();
curl_setopt($chh, CURLOPT_URL, $url_email);
curl_setopt($chh, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($chh, CURLOPT_POSTFIELDS, 'data=' . $str_data); // `data` moved here