SSO doesn't work

### Steps to reproduce

_Disclaimer: I'm not a specialist and don't know exactly how Matrix (Synapse) talks with the Element Client, so there's a possibility of a noob question below._

### **1. Where are you starting? What can you see?**
I have a YunoHost server, running Synapse. Login with user/password is disabled in the configs, and only is possible to login using SSO.

With Element Android, when you click to login with SSO, Element opens up a web page with **YunoHost's SSOwat**, asking for the username and password, and after the authentication, it works perfectly.

With Element iOS, the login with SSO doesn't even show up, and it throws this error:

I'm not sure if this is pertinent, but this is the URL that is opening up when the SSO loads (on iOS):
`https://invaliddomain.tld/_matrix/client/r0/login/sso/redirect/?redirectUrl=element://connect?transaction_id%3Dm56[CENSORED]`
_I've added the [CENSORED] tag because I'm not sure if that thing is an auth token or something like that._

### **2. What do you click?**
"Login with SSO" button after setting Element to use my homeserver.

### Outcome

#### What did you expect?
I expected Element to login after YunoHost's SSO authentication.

#### What happened instead?
An error showed up.

### Your phone model

iPhone 13 Pro Max

### Operating system version

iOS 16.0.2

### Application version

Element version 1.9.7

### Homeserver

Synapse 1.67.0 Stable

### Will you send logs?

No

Start by reproducing the “Login with SSO” flow on Element iOS 1.9.7 against Synapse 1.67.0 with YunoHost SSOwat, then inspect the /_matrix/client/r0/login/sso/redirect/ entry point and its element://connect redirect. Compare the iOS behavior with the working Element Android flow; done means iOS completes authentication and logs in without the reported error.

Written by the indexing model from the issue text.