to append api script to body add this in the head that's the only option

<script>
document.addEventListener('DOMContentLoaded', function () {
    var fhScript = document.createElement('script');
    fhScript.src = 'https://fareharbor.com/embeds/api/v1/?autolightframe=yes';
    document.body.appendChild(fhScript);
  });
</script>