SD card file transfer android marshmallow airdroid web app

Unable to transfer files directly to sdcard using airdroid web app and android 6 marshmallow.
The sdcard wasn't detected automatically so I added it's path but I could not edit anything in sdcard using webapp even though I have given the airdroid android app write permissions on the sdcard.
When I try to upload anything on the sdcard it gives an error file too big.
Please Help

Hi,could you please tell us the phone model , Android OS version and AirDroid version? Also, it would be helpful for troubleshooting the issue if you can send us a screenshot of it.Thx