[Bug]: Quicksy - Registration of new users not working on IPhone

### What Monal Release channel are you using? AppStore ### iOS system version (if applicable) _No response_ ### macOS system version (if applicable) _No response_ ### Monal version 1.21.0 ### Used XMPP server (domain) quicksy.im ### Which XMPP-Server software are you using? None ### XMPP Server Software Version _No response_ ### How many accounts are you using in Monal? 1 ### What happened? Hello, I tried to move a group of friends to Quicksy (a great low-barrier-XMPP-entry point for low-tech-users in my opinion - Thank you!). The android users could install and join fine. For the IPhone users however, the attempt stops at the screen where the Phone asks for confirmation to start verifying the number. The users cannot click either of the two buttons (OK <for starting the number verification>, CHANGE <for changing the number>). Neither of the buttons works, or the server response is not happening. For the user, just nothing happens when trying to click either button. I also placed this issue at the quicksy-server-side (https://codeberg.org/iNPUTmice/QuicksyServer/issues/11#issuecomment-12499365). From there I was referred here. Thank you! ### Anything else? _No response_ ### FAQ - [x] I have [checked the FAQ](https://github.com/monal-im/Monal/wiki/FAQ---Frequently-Asked-Questions) for my issue ### Considerations for XMPP users - [x] I have checked if my issue can be solved with [Considerations for XMPP users](https://github.com/monal-im/Monal/wiki/Considerations-for-XMPP-users) and [Considerations for XMPP server admins](https://github.com/monal-im/Monal/wiki/Considerations-for-XMPP-server-admins) ### XEP-Check - [x] I have checked that at least XEP-198, XEP-0280, XEP-0352, XEP-0357, XEP-0313 and XEP-0163 are activated on my server and shown as 'green' under Settings --> Account--> (i) in advanced settings ### Notifications-Menu - [x] I have checked that all checkmarks are present under Settings --> Notifications