Passing a List to a ServerConnect using "IN"

Hello Wapplers,

I’m filtering a query based on a form, which passes the value of a dropdown to a SC through GET. Regular stuff.
The query works when a single letter is passed, i.e. C or U, but returns empty when the default value of C,U is passed.

Here is the searchrole form element.

And the query uses “IN” as I want both letters to be found and the whole list of people returned. (leaving it empty and passing nothing/Null doesn’t work either

Any idea how to make this work?