The service that Minehut uses to process downloads is, as always, down (I really hope they change it soon, because this is getting a bit ridiculous). There's really nothing that can be done with this, I'm afraid you'll just have to wait.
As for your problem with the Citizens plugin: it hasn't been updated since January, 2019 and the latest supported version is 1.13.2. Sadly, you'll have to wait until the plugin developers release an update which supports the latest version, and Minehut add the updated release.