@foreach($subcategories as $subcat)
<li>
    <div class="custom-control custom-checkbox">
        <input type="checkbox" 
            class="custom-control-input"
            id="{{$subcat->id}}" name="subcategories[]"
            value="{{$subcat->id}}"{{$selectedSubCategories && in_array($subcat['id'], $selectedSubCategories) ? 'checked' : ""}}>
        <label class="custom-control-label"
            for="{{$subcat->id}}">{{$subcat->title}}</label>
    </div>
</li>
@endforeach