CURL got Could not resolve host: my subdomain

Question

I'm using wordpress and I installed jwt.

My WordPress is installed on sub domain and I want to call jwt from the main domain.

when I call this URL from postman:

https://subdomain.domain.com/wp-json/jwt-auth/v1/token

it returns a response but when I call this URL from inside my main domain:

$url = 'https://subdomain.domain.com/wp-json/jwt-auth/v1/token';


$data = array(
    'username' => '***',
    'password' => '***'
);

$data_string = json_encode($data);

$ch = curl_init($url);
curl_setopt($ch, CURLOPT_CUSTOMREQUEST, "POST");
curl_setopt($ch, CURLOPT_POSTFIELDS, $data_string);
curl_setopt($ch, CURLOPT_SSL_VERIFYHOST, 1);
curl_setopt($ch,CURLOPT_SSL_VERIFYPEER ,1);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
    'Content-Type: application/json',
    'Content-Length: ' . strlen($data_string))
);

$result = curl_exec($ch);
if (curl_errno($ch)) {
    $error_msg = curl_error($ch);
}
curl_close($ch);



die("dd".$result.$error_msg);

it returns:

ddCould not resolve host: subdomain.domain.com 

My DNS config:

A @ myip
CNAME www maindomain
A subdomain myip

where is the problem?