pewc_filter_validate_cart_item_status.php

<?php
/**
 * Custom validation for add-on fields
 */
function prefix_filter_validate_cart_item_status( $passed, $post, $item ) {
	// pewc_group_3990_4033 is the ID of the field
	if( isset( $post['pewc_group_3990_4033'] ) && floatval( $post['pewc_group_3990_4033'] ) < 10 ) {
		wc_add_notice( 'My validation message', 'error' );
		$passed = false;
	}
  return $passed;
}
add_filter( 'pewc_filter_validate_cart_item_status', 'prefix_filter_validate_cart_item_status', 10, 3 );