Does the message appear in delta.chat? You have to click on it in deltachat desktop.
The alternative would be importing the backup from Android and importing it in the desktop application, but unfortunately that way is currently broken: https://github.com/deltachat/deltachat-desktop/issues/763
PS: sorry for the late answer, I wasn’t realizing that the email reply isn’t available (yet) on this discourse forum. (Meta: Please enable Email response to forum topic)