Hey, this sadly wouldn’t work with this plugin as it is extremely light weight and doesn’t support that feature.
There’s plenty of other plugins that would be able to help you with this. A quick Google of ‘WooCommerce Donations’ will bring up quite a few results.
Add the following script onto the cart page and it’ll prevent it from happening.
<script>$('.wdgk_donation').keyup(function () {
if (!this.value.match(/[0-9]/)) {
this.value = this.value.replace(/[^0-9]/g, '');
}
});</script>
