Unable to connect with app

Good evening, i’m new in this forum.
I have HA installed on a mini pc, everything works fine. I do connect only from my local network. I use the app from my ipad and iphone.
Since a few days, if i try to login on my iphone i get the message: “unable to connect to Home Assistant” retrying in xx seconds
On my ipad everything works fine.
When i use safari to connect, i get the same message, no matter which browser i use.
What to do?
Appriciate your help
Thx
John