Unfortunately, we know this issue, for some reason the app is uploaded from our side but only available as an update, not as a direct purchase.
We have applied to Apple developer helpdesk with our claim, but until they solve the issue we have a solution for those who have purchased OrthoGraph Architect earlier, as the app despite not being visible in the store is still available as an update.
1. Open the AppStore App on your device
2. Tap on the bottom the 'purchased' icon
3. You should see now two search field on the top. Use the one on the left labeled as 'Search Purchased Apps', type OrthoGraph there.
4. Now there should appear the FloorPlan app
5. Tap on the small cloud icon after the name of the app
6. Now the app is downloading
7. When it is downloaded, you can close the Appstore app, and start your updated OrthoGraph
Please watch this video where we have explained it: http://youtu.be/F0OhWUK7CAg
Unfortunately due to this Appstore anomaly we have customers who succeeded to update this way and others who did not, including some devices of our own here in the office. I will come back as soon as we could push Apple to solve the issue. In case if you fell in the second group, there is still a solution - but it costs data loss, as the old projects would be lost this way. If it is not a problem for you, or you also have OrthoGraph Cloud account where you can backup, you can delete the old app then you will be able to download above way the update.