[Unity 2020.3.22] UnityWebRequest.Get(url) not working on iOS

Hi everyone, we just migrated from unity 2018 to unity 2020 and found out unity web requests are not working anymore on iOS. We receive an error 500 when we make GET requests to a Cloudflare server.

This is our code:

  using (UnityWebRequest www = UnityWebRequest.Get(tileUrl))
 {
       UserSecurityToken.AddSecurityTokenHeaders(www);
       www.timeout = StaticConf.WebServices.TileDownloadTimeout;
       yield return www.SendWebRequest();
       /* more code here */
 }

Analyzing the requests we found that compiled apps (Android and iOS ones) are sending the very same requests including the same headers except for one: iOS version is also including the header "content-length : 0".

Simulating the request via POSTMAN we are seeing that everything goes smooth without that header. Can you help us?

Thanks in advance.