Unfortunately, `acct` is not one of the prefixes that can be used that way. I'd like to ask the WHATWG to add it to the list of protocols that can be used, but I wanted to have a demonstration app first that would show it. So, I made a site to test out the registration. I couldn't use `acct`, so I made it work with `web+acct`, which is how you can work with protocols not on the allow list.