Add "IsAccessibleForFree" to the Article schema

IsAccessibleForFree.php

/**
 * Add the 'isAccessibleForFree' property to Yoast's Article schema.
 *
 * @param array $data The Article schema data.
 * @return array The modified schema data.
 */

function add_is_accessible_for_free_to_article_schema( $data ) {
    // Set the property to true. You can change this to false if needed.
    $data['isAccessibleForFree'] = true;

    return $data;
}
add_filter( 'wpseo_schema_article', 'add_is_accessible_for_free_to_article_schema' );