Onboarding users and registering with a registration token not working form IOS

### Your use case

#### What would you like to do?

I configured my synapse to allow signup, but require a registration token. I tried that process through the IOS element app, and failed to sign up successfully.

This is my synapse/homeserver.yml config :
```
...
enable_registration: true
registration_requires_token: true
```

#### Why would you like to do it?
I would like to be able to allow non-precreated users to easily sign up to the chat. The idea is to provide a Link or QR code that people can use to start the process.

This would allow to codify the correct server and the registration token within the URL as parameters. ( right?)

This is the URL that I'm using / clicking on IOS using my onPrem instance :

"https://element.lutz.sales-demos.element.io/?hs_url=element.lutz.sales-demos.element.io&token="

#### How would you like to achieve it?

Using the Sign up URL, you don't need to select the server. The token allows for my gated access.

ISSUE:

It does not work. See the screenshot here :




### Have you considered any alternatives?

_No response_

### Additional context

_No response_

### Are you willing to provide a PR?

No