Input type='text' value not fetched through id in a loop

I'm doing something wrong and I don't know what's that. I'm trying to fetch text from input field through id, and the input field is within a while loop as there are multiple input fields. Here is my code:

if($count22->num_rows>0){               
    while($row = $count22->fetch_array()){      
        $mail = $row['UserMail'];
        $comment = $row['Comment'];
        $comment_id = $row['ID'];
        // Reply input field starts 
        echo "<input type='text' name='reply' id='reply' placeholder='Enter Reply here' min='5' max='100' class='big-input' style='width:40%;margin-left:40px;margin-right:40px;'>";

        echo "<button class='btn btn-outline-info' onclick='InsertReply($comment_id)'>Reply</button>";
    }        
}

On clicking button, InsertReply function is called where input field is checked whether it is empty or not.

InsertReply() function:

function InsertReply(x) {
    alert("Insert Reply Function Called! with comment id : " + x);
    //Storing values in variables
    var reply = document.getElementById("reply").value; //Error Here, not accepting reply
    var mail = document.getElementById("mail").value;
    var p_id = document.getElementById("postid").value;
    if (reply.length == 0) { //If user has entered nothing
        alert("You Entered Nothing!"); //Show message
    }
}

The issue is that it is fetching text from only first input field, it is showing alert box 'You entered nothing' for the rest of the input fields even if I enter text. Let me know if you have any queries, any alternative solution/suggestion will be highly appreciated!