cerebrate/templates/element/genericElements/Form/multiFieldButton.php

<?php
$seed = 'mfb-' . mt_rand();
?>
<div class="d-flex align-items-center">
    <?php
    $content = sprintf('<a class="btn btn-primary btn-xs">%s</a><a class="btn btn-link btn-xs">%s</a>', $this->Bootstrap->icon('plus'), __('Add another {0}', h($metaTemplateFieldName)));
    $content = sprintf(
        '%s%s',
        $this->Bootstrap->button([
            'nodeType' => 'a',
            'icon' => 'plus',
            'variant' => 'secondary',
            'size' => 'xs',
        ]),
        $this->Bootstrap->button([
            'nodeType' => 'a',
            'text' => __('Add another {0}', h($metaTemplateFieldName)),
            'variant' => 'link',
            'class' => ['link-secondary'],
            'size' => 'xs',
        ])
    );
    ?>
    <?=
    $this->Bootstrap->button([
        'id' => $seed,
        'html' => $content,
        'variant' => 'link',
        'size' => 'xs',
    ]);
    ?>
</div>

<script>
    (function() {
        $('#<?= $seed ?>').click(addNewField)

        function addNewField() {
            const $clicked = $(this);
            let $lastInputContainer = $clicked.closest('.multi-metafields-container').children().not('.template-container').find('input').last().closest('.multi-metafield-container')
            if ($lastInputContainer.length == 0) {
                $lastInputContainer = $clicked.closest('.multi-metafields-container').find('input').last().closest('.multi-metafield-container')
            }
            const $clonedContainer = $lastInputContainer.clone()
            $clonedContainer
                .removeClass('has-error')
                .find('.error-message ').remove()
            $clonedContainer
                .find('label.form-label').text('')
            const $clonedInput = $clonedContainer.find('input, select')
            if ($clonedInput.length > 0) {
                const injectedTemplateId = $clicked.closest('.multi-metafields-container').find('.new-metafield').length
                $clonedInput.addClass('new-metafield')
                adjustClonedInputAttr($clonedInput, injectedTemplateId)
                $clonedContainer.insertAfter($lastInputContainer)
            }
        }

        function adjustClonedInputAttr($inputs, injectedTemplateId) {
            $inputs.each(function() {
                const $input = $(this)
                let explodedPath = $input.attr('field').split('.').splice(0, 5)
                explodedPath.push('new', injectedTemplateId)
                dottedPathStr = explodedPath.join('.')
                brackettedPathStr = explodedPath.map((elem, i) => {
                    return i == 0 ? elem : `[${elem}]`
                }).join('')
                $input.attr('id', dottedPathStr)
                    .attr('field', dottedPathStr)
                    .attr('name', brackettedPathStr)
                    .val('')
                    .removeClass('is-invalid')
            })
        }
    })()
</script>