Ive inputed all the correct values into the three fields the action has available:
Document Set Name - gave it a name of "Agenda_005" (I tried without the "_" and had same error
Target List - Pointed it to the absolute URL of the library and also tried the name "Shared Documents"
SharePointSite URL - Pointed it to the absolute URL of the site
I've enabled Document Sets on the library and even have one in there saved. The error I get is:
"Expression value is invalid. Specified value has invalid Control characters."