Same here,
while we wait for the fix if you are able to edit the plugin files you can check the code of the file
and replace the _fee_amount in the line 221 to _name_percent
payment-method-checkout-fee-for-woocommerce/checkoutfee.php
221? ? ? ??$fee_amount?=?get_option($method_id?.?‘_fee_amount’);
221? ? ? ??$fee_amount?=?get_option($method_id?.?‘_name_percent’);