Jerome Lopez

I managed to log the wp error on wordpress_users.php if is_wp_error($user_id):

 $error_code = array_key_first( $user_id->errors );
	        $error_message = $user_id->errors[$error_code][0];
           // $log = wp_kses_post("Echec de la création du compte pour l'adresse" . $adh['mail'] . '</br>'); 
            $log = wp_kses_post("Echec de la création du compte pour l'adresse" . $error_message . '</br>'); 

I found the erro it was due that I didn’t use the good “Identifiant”.
It should be mail and not email.
Sorry to waste your time