SQL/Php how to send one variable to database - Think it's a syntax error!

My database has been working well until I tried sending only one variable. It seems to me like its a syntax error but I can't seem to find an example using only one variable. Thanks in advance!

I am mostly suspicious of my php

  if($_REQUEST['action']=="submit_user_name") 
   {
         $name = $_REQUEST['name'];
         $sql = "INSERT INTO user_name (name) VALUE ('$name')";
         //mysql_query($query);
         $result = mysqli_query($connect, $sql);
   } 

Here's my Unity code:

  WWWForm submitUser = new WWWForm();
         submitUser.AddField("action", "submit_user_name");
         submitUser.AddField("name", userName);
         WWW sendData = new WWW(url, submitUser);
         yield return sendData;
 
         if (sendData.error != null)
         {
             print(sendData.error);
 
         }
 
         yield return sendData;
 
         Debug.Log(sendData.error);