Limitations

Unigram Mobile has some limitations and trade offs.

Answer directly from Notification

You may answer directly from notifications. It is wise to use this feature only for short answers as TDlib only sends new messages if all messages have been synchronized (aka downloaded).

If not everything has been downloaded already, the message does not get sent. There is no backup or try again later implemented as apps can only run for short times in the background. Unigram Mobile does not sync everything when a new notification arrives to save battery.

Feel free to implement a better solution (or just improve it) and submit it as a pull request, please.