I have a new M210 RTK which has never flown and I'm using a CrystalSky. After booting everything up in the proper order and starting DJI Pilot, which is updated to the functional (non-beta) version, I have a Cannot Take Off message in the upper left-hand portion of the screen.  There is no clue in the App as to why.  Going down the checklist, all parameters indicate "normal."  
I have re-calibrated the IMU and compass, just to be sure.  There is no "Aircraft Locked" message, as I seen reported elsewhere on this forum, nor is there any indication of a battery problem. I've updated the firmware of both aircraft and batteries.
I do find a "WEAK RTK SIGNAL" message.

I do live about 2 miles from a medium-sized airport - Class E airspace and I know that my No-Fly-Zone data is upt to date.  Could the problem be that simple (although there is no specific indication of that issue in the app) or am I looking at another problem?

First confirm with DJI if you can use your particular drone with DJI Pilot. I lost my Spark while using it and they refuse to open a case, even to see whether there was a problem by studying the DJI GO 4 information.

The app does not tell you which drones are compatible with it, nor will your drone warn you not to use it.

DJI have told me it's a third party app, it's not compatible with Spark and also that they can't open a case because they can't get the data from Pilot, even though I sent them the Pilot flight data via Google Drive.

DJI WILL find all sorts of excuses not to open a case if you use the Pilot app.

DJI Pilot is a third-party app?  wha....???

Naturally this drone will not take off without solid satellite lock, which must be established prior to. In this case RTK system is responsible for such, therefore weak signal issue must be solved first.

it is normal, if you fly without the station, it is enough to click on the icon of the satellites and to deactivate the rtk