alexandreP-37

if ( empty( $values ) && $source_element_id ) {
    $this->sitepress->sync_custom_field( $source_element_id, $post_id, $meta_key );
}

if ( ! get_post_meta( $post_id, 'copyoncedone' ) == 1 ) {
            add_post_meta($post_id, 'copyoncedone', 1 );
            foreach ( $custom_fields_to_copy as $meta_key ) {
                $values = isset( $custom_fields[ $meta_key ] ) ? $custom_fields[ $meta_key ] : [];
                if ( ! empty( $values ) ) {
                    $values = array( $values );
                }
                $values = apply_filters(
                    'wpml_custom_field_values',
                    $values,
                    [
                        'post_id'                   => $post_id,
                        'meta_key'                  => $meta_key,
                        'custom_fields_translation' => WPML_COPY_ONCE_CUSTOM_FIELD,
                    ]
                );
 
                if ( empty ( $values ) && $source_element_id ) {
                    $this->sitepress->sync_custom_field( $source_element_id, $post_id, $meta_key );
                }
            }
}