Oh, WP8.1... I had ever used it always and loved it:)
Do you have any plan to update it to Windows 10 Mobile?
If you do so, the app will draw your phone screen:)
I use a Lumia 820 with WP8.1 and a Lumia 1020 with W10M, both phones not working with the updated app from you, the previous version worked with the Lumia 1020. It is a pity that the app is not compatible with WP8.1, because this is the most important thing for me, because I don't use W10M productively.