Hello,
This may happen because the application is not published with Microsoft yet. We plan to publish the application some time this year, so this warning will not happen once we do that.
You should still be able to run the application though. There is usually a "more info" or a "advanced" button on that dialog, then click the button that is called something like "run anyway". There should also be a checkbox for always allowing it to run. If this is not the case for you, could you send us a larger screenshot showing the entire dialog?
Thanks,
Utterly Voice team