Login step 2 not working

[PhilippFoerster]

Hey, I'm having trouble getting the access token...
This is the request that is sent from manual input via the browser:


And this is the one I am sending:


The only difference is the cookie... Doing it via the browser, there is one additional field: bm_sv
It is not documented anywhere and I can't find it in any code samples that claim to have a working login. Does anyone have an idea if that is the reason for it not working or if it is something else I haven't noticed?
It is also not provided as Set-Cookie in the first request :(