I'm trying to do a curl post from php:

https://api.wmspanel.com/v1/realtime_data?client_id=aaa&api_key=bbbb&data_slice=ccc

These are the options:
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_POSTFIELDS, $hashesJson);
curl_setopt($ch, CURLOPT_IPRESOLVE, CURL_IPRESOLVE_V4);
curl_setopt($ch, CURLOPT_HTTPHEADER, array(
'Content-Type: application/json',
'Content-Length: ' . strlen($hashesJson))
);
$hashesJson is json string.

I get the following error on the server:
Could not resolve host: api.wmspanel.com

P.S.:
If I try to do a call in the browser like this:
https://api.wmspanel.com/v1/routes?client_id=aaa&api_key=bb
The api responds correctly.
The ip of the server is whitelisted.

Any ideas why ?

"Could not resolve host: api.wmspanel.com" means your dns on the server cannot resolver api.wmspanel.com host name. Please setup server correctly. You can try to access any other public web resource to check your server setup e.g curl -vvv https://wmspanel.com