Does it matter if the US Mission sends a notification letter before the lawsuit?

It doesn't matter if there is a problem with the pro-notification. It is a collection method of a third-party debt collection company entrusted by Meituan, with the purpose of intimidating you. Just pay it back quickly. Meituan's online lending is a private lending relationship. There is no criminal responsibility and it will not go to jail. If Meituan sues you, you will receive a subpoena from the court, not these so-called notification letters or lawyer letters. These letters have no legal effect.