Only one device can't connect to my sonos amp

Hello,

A family member came into my house today with their iPhone 8, but could not connect to my sonos controller.

Here is everything that i've checked / tried :

• The iPhone (and all other successfully connected device) are on the same network, using the app version 11.15.4 (my phone) or 11.15.5 (the iphone).
• I made sur the app on the iPhone had all the permissions.
• I double checked that all devices were indeed connected on the same network. Not that it matters, but both the iphone and the amp are on 2.4GHz (my phone is connected on the 5GHz band)
• I uninstalled / reinstalled the app on the iphone 
• And finally, I removed and added back the wifi network on the iphone.

Unfortunately,  none of this worked. Any new idea or explanation would be welcome.

I searched on this community for related topics, but could not find anything I did not try.

Have a great day.