I checked the documentation but the checkbox validation example works for only one box. I want to validate a group of checkbox where at least one of them must be selected.

My code works fine for my requirements. If you have better suggestion I'm happy to try .

Thanks for your opinion. I don't know, but the snippet works fine. I've a group of checkbox where at least one has to be checked before submit the form. In my case if a box is checked the required is satisfied so I remove the required property from all checkbox. If no box is checked the required property is applied to all checkbox.

I started with the page you link, but there aren't example about checkbox group, there are only single checkbox validation.

  <div class="form-row">
                        <div class="custom-control custom-checkbox mb-3">
                            <input type="checkbox" class="custom-control-input" id="my_match3" name="nsdc" required value="Negative staining data collection" onchange="checkRequired();">
                            <label class="custom-control-label" for="my_match3">Negative staining data collection</label>
                            <div class="invalid-feedback">Select at least a service.</div>
                        </div>

                    </div>
                    <div class="form-row">
                        <div class="custom-control custom-checkbox mb-3">
                            <input type="checkbox" class="custom-control-input" id="my_match4" name="cemsv" required value="Cryo-EM specimen vitrification on Vitrobot MkIV (9 grids max)" onchange="checkRequired();">
                            <label class="custom-control-label" for="my_match4">Cryo-EM specimen vitrification on Vitrobot MkIV (9 grids max)</label>
                            <div class="invalid-feedback">Select at least a service.</div>
                        </div>

                    </div>
                    <div class="form-row">
                        <div class="custom-control custom-checkbox mb-3">
                            <input type="checkbox" class="custom-control-input" id="my_match5" name="cemgs" required value="Cryo-EM grids screening (9 grids max)" onchange="checkRequired();">
                            <label class="custom-control-label" for="my_match5">Cryo-EM grids screening (9 grids max)</label>
                            <div class="invalid-feedback">Select at least a service.</div>
                        </div>

<script>
function checkRequired() {
    if ($('input[type=checkbox]:checked').length > 0) {  // the "> 0" part is unnecessary, actually
        $('input[type=checkbox]').prop('required', false);
    } else {
        $('input[type=checkbox]').prop('required', true);
    }

}

I did it with a snippet of js code.