"We encountered a pro​blem processing your request" when downloading ISO from Windows Insider Program

Question

I'm trying to download an ARM version of Windows to use within Parallels on my Apple Silicon MacBook Pro, as described in this article. I signed up for the Windows Insider Program and navigated to the page where I could download the ISO files, and select the edition and the language I wanted:

A popup follows saying 'Validating your request' with an indication that it might take several minutes, but quite soon it stops and gives me an error: "We encountered a problem processing your request", with a link to a very broad FAQ.

Answer 1

It turned out that somehow, my login from the Insider Program sign up didn't carry over to the download page, and it's publicly accessible. Even when you're not logged in, it allows you to select an edition, so it seems to work, but it doesn't.

After signing in, I was able to start the download.

_{I'm not sure if other users have the same sign in problems as me, or if I was just unlucky; however, I could conceive situations where I'd send the link to the download page to someone else who is not logged in yet.}