Hi Yusuke,
I can not reproduce this issue when using the Account Activity API (AAA) to deliver the DM events, i.e. the AAA returns the “quick_reply_response” object and complete metadata. Just tested with the @SnowBotDev bot account…
I am not aware of any DM API issues at this time… Let me check on a few things on our side and get back to you.
Thanks!