Accordion panel extra expand

Our website uses an accordion with collapsible panels. Inside one of the accordion panels there are a couple of checkboxes that can be checked or unchecked. Checkbox 1 -if checked- shows another set of two checkboxes but the accordion panel does not expand when the hidden checkboxes show.

How do I make the accordion panel also expand when the new checkboxes appear?

The below HTML + CSS + JS is being used.

// Accordion panels
    var acc = document.getElementsByClassName("troubleshooter-accordion");
    var i;
    for (i = 0; i < acc.length; i++) {
      acc[i].addEventListener("click", function() {
        this.classList.toggle("active");
        var panel = this.nextElementSibling;
        if (panel.style.maxHeight) {
          panel.style.maxHeight = null;
        } else {
          panel.style.maxHeight = panel.scrollHeight + "px";
        } 
      });
    }
// Hide checkboxes
    function showextra() {
      var checkBox = document.getElementById("check1a");
      var extra = document.getElementById("checkbox1a-extra");
      if (checkBox.checked == true){
        extra.style.display = "block";
      } else {
        extra.style.display = "none";
      }
    }

.troubleshooter-accordion {
    background-color: rgba(0,175,75,1.00);
    border: 1px solid rgba(0,175,75,1.00);
    color: rgba(255,255,255,1.00);
    padding: 16px;
    cursor: pointer;
    width: 100%;
    text-align: center;
    outline: none;
    font-size: 1.15em;
    transition: 0.4s;
    margin-top: 2px;
    border-radius: 8px;
}
.active, .troubleshooter-accordion:hover {
    background-color: rgba(255,255,255,1.00);
    border: 1px solid rgba(0,145,255,1.00);
    color: rgba(0,145,255,1.00);
}
.troubleshooter-panel {
    padding: 0 16px;
    background-color: white;
    max-height: 0;
    overflow: hidden;
    transition: max-height 0.2s ease-out;
    border-radius: 8px;
}
.troubleshooter-panel h4 {
    margin: 16px 0
}
.infobox {
    border: 2px solid rgba(0,175,75,1.00);
    border-radius: 8px;
    margin-top: 16px;
    padding: 24px 16px;
}
.checkbox-extra {
    display: none;
    margin-left: 24px;
}

        <button class="troubleshooter-accordion">Accordion</button>
        <div class="troubleshooter-panel">
          <h4 align="center">Check the boxes below</h4>
          <hr>
          <p>
            <label><input type="checkbox" id="check1a" name="check1a" value="check1a" class="check1a" onclick="showextra()">&nbsp; Checkbox 1</label>
            <div class="checkbox-extra" id="checkbox1a-extra">
              <p>
                <label><input type="checkbox" id="check1a1" name="check1a1" value="check1a1" class="check1a1">&nbsp; Checkbox 1-A</label><br>
                <label><input type="checkbox" id="check1a2" name="check1a2" value="check1a2" class="check1a2">&nbsp; Checkbox 1-B</label>
              </p>
            </div>
            <hr>
          </p>
          <p>
            <label><input type="checkbox" id="check1b" name="check1b" value="check1b" class="check1b">&nbsp; Checkbox 2</label>
          </p>
          <hr>
        </div>