Question Can't send POST requests from Unity, but it works on Postman

I've searched the problem, but didn't found any solution, even tough I've seen similar questions beign asked.
I'm receiving HTTP/1.1 500 Internal Server Error

In line 26, there is a Debug.log(txt), which is the string created from the JsonUtility.ToJson(). I copied this txt and pasted in Postman and it worked just fine. So I don't know what I could be doing wrong.

Thanks in advance.

Code (CSharp):

1. using System;
2. using System.Collections;
3. using UnityEngine;
4. using UnityEngine.Networking;
5.  
6. public class TEST : MonoBehaviour
7. {
8.     [Serializable]
9.     public class Player
10.     {
11.         public string name;
12.         public int score;
13.  
14.         public Player(string name, int score)
15.         {
16.             this.name = name;
17.             this.score = score;
18.         }
19.     }
20.  
21.     void Start()
22.     {
23.         Player p = new Player("MMM", 200);
24.         string txt = JsonUtility.ToJson(p);
25.  
26.         Debug.Log(txt);
27.  
28.         StartCoroutine(Post("valid url, same as used in postman", txt));
29.     }
30.  
31.     IEnumerator Post(string uri, string postData)
32.     {
33.         using (UnityWebRequest www = UnityWebRequest.Post(uri, postData))
34.         {
35.             yield return www.SendWebRequest();
36.  
37.             if (www.result != UnityWebRequest.Result.Success)
38.             {
39.                 Debug.Log(www.error);
40.             }
41.             else
42.             {
43.                 Debug.Log("Form upload complete!");
44.             }
45.         }
46.     }
47. }

 

After using Charles Proxy I could find the problem, then I found a solution searching online. Here's the updated code working fine (changes were only made to the Post IEnumerator):

Code (CSharp):

1. using System;
2. using System.Collections;
3. using UnityEngine;
4. using UnityEngine.Networking;
5. public class TEST : MonoBehaviour
6. {
7.     [Serializable]
8.     public class Player
9.     {
10.         public string name;
11.         public int score;
12.         public Player(string name, int score)
13.         {
14.             this.name = name;
15.             this.score = score;
16.         }
17.     }
18.     void Start()
19.     {
20.         Player p = new Player("MMM", 200);
21.         string txt = JsonUtility.ToJson(p);
22.         Debug.Log(txt);
23.         StartCoroutine(Post("valid url, same as used in postman", txt));
24.     }
25.     IEnumerator Post(string uri, string postData)
26.     {
27.         using (UnityWebRequest www = new UnityWebRequest(uri, "POST"))
28.         {
29.             www.SetRequestHeader("Content-Type", "application/json");
30.             byte[] rawData = Encoding.UTF8.GetBytes(postData);
31.             www.uploadHandler = new UploadHandlerRaw(rawData);
32.  
33.             yield return www.SendWebRequest();
34.             if (www.result != UnityWebRequest.Result.Success)
35.             {
36.                 Debug.Log(www.error);
37.             }
38.             else
39.             {
40.                 Debug.Log("Post data upload complete!");
41.             }
42.         }
43.     }
44. }