Problem with connecting to SignalR (Both 400 and 405) using Angular 17 and .Net Core v8

Frontend and backend: Using Angular 17 and .Net Core v8 (built by ebmonney/Quickapp).

1. Why, when one setup, according to Microsoft documentation, do one get Cannot POST problems, error 400? (Check answer 1)
2. Why, (after solving the above problem), do one get 405 errors METHOD NOT FOUND? Checking the F12 Network profile, it says it only allows "GET, HEAD", but it's asking for POST during negotiations, so is that really the problem?

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