I don’t know what is your purpose here.
I didn’t mean you need to buy anything. My point is just if you want to use a custom board, then you should check with the board vendor how to flash their board.
Generally they will provide their own package (mostly based on sdkmanager image but with modification to meet their hardware)
I just checked your post. The error you got there for now is just your host PC does not support IPv6.
IPv6 is disabled. Please enable ipv6 to use this tool
Error: ipv6: IPv6 is disabled on this device.
Error: ipv6: IPv6 is disabled on this device.
If you don’t fix this, then even getting a NV devkit will not help. The problem is the setting on your host PC, not Jetson.