Sorry can't help I've never use the app. But i would let the manger know and if that doesn't help then i would contact McDonald's corp.
Yeah, if you do anything besides walk up to the counter and ask for regular items and pay the regular way, you're gonna have to deal with irregular service. Best bet is asking in advance if the order taker knows how to do it, then asking for someone who can (good luck if it's busy).
Thanks! Your answer is awaiting moderation.