This is a suggestion to add a config value where you can choose if players are able to set a wager during a challenge.
This is probably not a main priority but this might be handy especially if there are server owners which want to disable if they don't want any kind of betting in their server.

If feel like this would be easy to add since it just checking if wagersAllowed is set to true in the config and returning a message that says the server doesn't allow wagers when they add a argument in their command (or just process the command as-is if you do allow it :). )