Mark, I had the same problem recently trying to set up my Fire HD8. Here is what I did.
The card must be formatted as external storage.
Settings-Security & Privacy-Allow Apps from Unknown Sources-Yes or button “on”
Most importantly- When I unzipped the ExploreStars file, I opened the ExploreStars
folder, and tried to load the 2 inclosed files separately on the HD card. I was trying to
copy the file path from the diagram on ES web site. Would not work.
Instead, just place the ExploreStars folder in the correct position on the HD card.
I did not rename any files, or attempt to place the file in photos.
Now when I go to Settings-Storage-SD Card Storage-Photos, it shows 79.00mb
for 338 items. The files were placed there automatically.
Now the app works fine. (I also have the IOS version on an ipad.)
Hope this helps. Harry
Vero Beach, FL
Scopes: ES AR102, Meade ETX 90 EC
Mounts: ES iExos 100-PMC Eight, (Using ExploreStars iPAD), Oberwerk 5000 Tripod
Binos: Oberwerk 15x70, 8x40