Finally at last I am able to pass cookies in wvdownloader and I am getting proper response now from amazon server.

But a big BUT lol yes, wvdownloader is now not able to recognize streams and I am clueless. I tried with old json files which I saved when it was working fine and surprisingly on those files also it is not able to recognize streams.

I am not able to understand what is fishy going on here hahahaha. Do PM me back if anyone knows anything about it.