I've just got this working on my new Lenovo A7-20 7 inch tab.
Like you, Google Play said my device was incompatible and wouldn't let me install.
First, tick 'allow unauthorised applications to run' beforehand though (somewhere in Settings) so the tablet will let you download apps from outside the Google Play store.
Then, using the UC Internet Browser (ie NOT Google Chrome), navigate to the DJI P3 site and click the Go App link; click the 'get it on Google' and it should just allow you to download it; you'll see the download at the top of the Tablet's screen.
This method worked fine for me 2 days ago (31Jan)
If you use Google Chrome it will navigate thru to the Play Store and you'll be going round in circles.
Cheers,
Ian