<div class="form-outline">

  <input type="text" id="custom-mask" class="form-control" data-mdb-input-mask="27ZG            " 

        data-mdb-custom-mask=" " data-mdb-custom-validator="[A-Za-z0-9]*"/>

  <label class="form-label" for="custom-mask">Custom mask</label>

</div>