To use a double-quote in switch value, you need to double it:

See https://winscp.net/eng/docs/scripting#quotes

Using winscp.com from the command line, with PKE:

Note the passphrase has a quote mark in it. If I type this in manually at the command line, it works fine. If I try and pass it in as a parameter, it always fails with "Wrong passphrase".

I've tried wrapping it in alternative quotes:

and also escaping it:

and even double escaping it:

All give "Wrong passphrase". There's no documentation that I can see as to what to do in these circumstances, so I'd hazard a guess it's either a bug in the software, or if there is an escape character, there's a bug in docs whereby the escape character/mechanism isn't commented (should be: https://winscp.net/eng/docs/scriptcommand_open#passphrase).

p.s. - thanks for the great work!