function custom_save_date( $post_id )
{
// get user from user field
$user = get_field( 'user', $post_id );
// get user id from user field
$user_id = $user['ID'];
// get date changed field
$date_changed = get_field( 'date_de_fin_dabonnement', $post_id );
$date = new DateTime( $data_changed );
// set format
$date = $date->format('d/m/Y');
// update user field
update_field( 'date_de_fin_dabonnement', $date, 'user_' . $user_id );
}
// acf save post hook
add_action('acf/save_post', 'custom_save_date', 15);
ACF has its own hook. You can use them for your fields. Also, you forgot the global $post as well as the user in your example. I have not tested the code AND sorry for my english! 🙂
If you using an other output from user field, just change the output in line 7 and 17.
Useful links:
acf/save_post
ACF user field (first answer from John)
