Attempting to request directions while adding cashTollOnly to the exclusions causes the request to fail with the following error.

Exclude value must be one of: toll, motorway, ferry, unpaved, cash_only_tolls, border_crossing, point(lon lat)

Example code snippet:

let routeOptions = NavigationRouteOptions(waypoints: waypoints, profileIdentifier: .automobile)
routeOptions.roadClassesToAvoid = [.cashTollOnly]

It looks like the string value being used is cash_only_toll, but the correct value is cash_only_tolls.