I have a WKWebView which should load the following url:
https://buchung.salonmeister.de/place/#offer-details-page?id=907599&venueId=301655
If you are in a sandboxed macOS app, you'll need to set the Outgoing Connections (Client) capability, you won't need to mess with Allow Abitrary Loads which shouldn't come into play for trusted https requests.
For iOS however, allowing client connections is the default, so you may need to implement WKNavigationDelegate
methods to handle security. Make sure you aren't just trusting untrusted certificates though. This Swift Talk video from objc.io is the best resource I know of, definitely worth 20 minutes if you're working in this area: https://talk.objc.io/episodes/S01E57-certificate-pinning