When i download firmware 3.10

continue to get  "Download Errror! Please Refresh '.....   also cannot use my DJI App any longer??

I assume you are referring to the Assist app?  I wonder if there heavy traffic is causing the issue due to the update being required.  It worked for me so you might want to just try at random times and see if it clears up.

By making the update mandatory they (DJI) kind of created a version of a DOS attack and the servers may be having a hard time keeping up.  I expect it will clear.