Wsrtjtyk

I've searched this issue for a while now and this is what I came up with, but it doesnt work:

<form action="Subscription.php" method="post">

     <label>field1<a style="color:red">*</a></label>

     <input type="text" id="field1" name="field1" pattern="^[A-Za-z -]+$" required>              



     <input type="checkbox" name="checkbox1" onclick="showMe('more'); togglerequirement();">Do you want more?



     <div id="more" style="display:none">

          <label>field2<a style="color:red">*</a></label>

          <input type="text" id="field2" name="field2" pattern="^[A-Za-z -]+$">

     </div>          

     <input type="submit" value="Invia richiesta di registrazione" class="btn" </form>



<script type="text/javascript">

function showMe (box) {

    var chboxs = document.getElementsByName("more");

    var vis = "none";

        if(chboxs[0].checked) {

            vis = "block";

        }

    document.getElementById(box).style.display = vis;

}



function togglerequirement(){

    var checkbox = document.getElementsByName("more");

    var field2= document.getElementsByid("field2");



    if(checkbox[0].checked){

        field2.setAttribute("required", "");

    }else{

        field2.removeAttribute("required");

    }

}

</script>

Before you say anything I've already tried with fiedl2.required; and it doesnt work either way.

What can I do?

You are trying to find checkbox by name "more". But it have name="checkbox1":

<input type="checkbox" name="checkbox1" onclick="showMe('more'); togglerequirement();">

I'ts working fine. But it changes second field to required when it's showing and not required when it's hidind. So, you do not see any effect.
not required here
required here

If I fully understand you, try this:

<form action="Subscription.php" method="post">

     <label>field1<a style="color:red">*</a></label>

     <input type="text" id="field1" name="field1" pattern="^[A-Za-z -]+$" required>              



     <input type="checkbox" name="more" onclick="showMe('more'); togglerequirement();">Do you want more?



     <div id="more" style="display:none">

          <label>field2<a style="color:red">*</a></label>

          <input type="text" id="field2" name="field2" pattern="^[A-Za-z -]+$">

     </div>          

     <input type="submit" value="Invia richiesta di registrazione" class="btn" </form>



<script type="text/javascript">

function showMe (box) {

    var chboxs = document.getElementsByName("more");

    var vis = "none";

        if(chboxs[0].checked) {

            vis = "block";

        }

    document.getElementById(box).style.display = vis;

}



function togglerequirement(){

    var checkbox = document.getElementsByName("more");

    var field2 = document.getElementById("field2");



    if(checkbox[0].checked){

        field2.setAttribute("required", "");

    }else{

        field2.removeAttribute("required");

    }

}

</script>