Configure Callback URL

In me here on Auth0 configured application dialog I am always failing to save the Callback URL.
I write, click on save changes. On reloading that dialog the Callback URL is still empty.

  1. Is this an issue of the testing account?
  2. Is there another hint to be mentioned?
    (Same with Allowed Callback URLs and Allowed Logout URLs)
    Thanx in advance

Any error message / error box at the top of the screen? If not, any error in the developer console of your browser?

Is it a valid URL pattern you’re entering? No wildcards or special kind of URLs that might be not be accepted?
Can you post the URL pattern you’re entering (no need to disclose the real domain name)