Domain in Ionos cannot be connect/redirect to my fly-app, when using Ipv4 and Ipv6 DNS of Ionos. Errot: ERR_CONNECTION_CLOSED

Hello,
i created a new App in Fly.io and have used his Ipv4 and Ipv6 in Ionos in order to redirect the domain-name to my app but it is not working. when i enter the domain name in the browser i received the following error “ERR_CONNECTION_CLOSED”
In the pass i used the same method for the first app, i created and all things worked fine during one year, but now the same method doesn’t work for my new created app (The old app has a problem, and i need to created a new app according to fly.)
Can someone help me ?