The Jetpack 3.1 download link is dead!

https://developer.nvidia.com/embedded/dlc/jetpack-l4t-3_1, The Jetpack 3.1 download link is dead, update please.

Not sure where you snagged that link from, but there’s an extra comma in that URL. Link without it works:
https://developer.nvidia.com/embedded/dlc/jetpack-l4t-3_1