WPML Custom end point link 2 existing translation

link_post_translation.php

<?php

/**
 * Link the FR translation and the EN translation
 * Called by API https://domain.com/wp-json/link_translation/post/
 */
function custom_rest_link_translation($data) {
    
    //Source https://wpml.org/wpml-hook/wpml_set_element_language_details/

    
    $inserted_post_ids = array(
        'original' => $data['original'],
        'translation' => $data['translation']
    );
 
    if ( $inserted_post_ids) {
        // https://wpml.org/wpml-hook/wpml_element_type/
        $wpml_element_type = apply_filters( 'wpml_element_type', 'post' );
         
        // get the language info of the original post
        // https://wpml.org/wpml-hook/wpml_element_language_details/
        $get_language_args = array('element_id' => $inserted_post_ids['original'], 'element_type' => 'post' );
        $original_post_language_info = apply_filters( 'wpml_element_language_details', null, $get_language_args );
         
        $set_language_args = array(
            'element_id'    => $inserted_post_ids['translation'],
            'element_type'  => $wpml_element_type,
            'trid'   => $original_post_language_info->trid,
            'language_code'   => 'en',
            'source_language_code' => $original_post_language_info->language_code,
            'check_duplicates' => true
        );
 
        $value = do_action( 'wpml_set_element_language_details', $set_language_args );
        echo "linked";
    }
}


add_action('rest_api_init', function () {
    register_rest_route('link_translation', '/post', array(
        'methods' => 'POST',
        'callback' => 'custom_rest_link_translation',
    ));
});