Did you keep the box it came in? I expect the SN is printed on there somewhere (most likely a sticker on the box).
Edit: meh, too slow...
Edit: meh, too slow...
Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
I tried the number on the box it didn't work and it asked for model name and s/n the s/n on the box didn't workIt should be on the box also if you still have it. Haven't tried using Kies with a Sprint phone so it may ask for either your SN or IMEI number. It is a two step verication process that Kies uses to download the correct firmware. Model and SN or IMEI.
the part that's not working is the s/nIt took me a few tries to figure out that you have to type model number all upper case.
SM-G920P
Then it should prompt you for SN.
I use odin to do it rightI have had the same issue with a Samsung Tracphone. You could try a different download of the stock firmware. Sammobile takes a long time for the free download but never had a issue flashing.
http://www.sammobile.com/firmwares/download/60059/G920PVPU3BOJ7_G920PSPT3BOJ7_SPR/