field_amount_smart_tag.php

<?php
/*
Display raw payment field amount with smart tag.
Usage:
- add code below to functions.php of your theme
- use smart tag `{field_amount="x"}` where x is the field ID from which you want to retrive raw amount without currency symbol etc.
*/

add_filter( 'wpforms_smarttags_get_smart_tag_class_name', 'get_amount_class_name', 10, 1 );

function get_amount_class_name( $class_name ) {

  if ( 'field_amount' === $class_name ) {
    return 'My_Amount_Smart_Tag';
  }
}

add_filter( 'wpforms_smart_tags', 'add_custom_smart_tag', 10, 1 );

function add_custom_smart_tag( $tags ) {

$tags['field_amount'] = "Field raw amount";

return $tags;
}

add_filter( 'wpforms_pro_smarttags_get_smart_tag_class_name', 'get_smart_tag_class_name', 10, 2 );

function get_smart_tag_class_name( $class_name, $smart_tag_name ) {

	if ( 'field_amount' === $smart_tag_name ) {
		return 'My_Amount_Smart_Tag';
	}

	return $class_name;

}

 add_action( 'wpforms_loaded', function() {

		class My_Amount_Smart_Tag extends WPForms\SmartTags\SmartTag\SmartTag {

			public function get_value( $form_data, $fields = [], $entry_id = '' ) {

				$attributes = $this->get_attributes();

				if ( ! isset( $attributes['field_amount'] ) || $attributes['field_amount'] === '' ) {
					return '';
				}

				return isset( $fields[ $attributes['field_amount'] ]['amount'] ) ? $fields[ $attributes['field_amount'] ]['amount'] : '';
			}
		}

 	}
);