This error occurs when the app creation request exceeds the default 100-second HttpClient timeout, usually due to temporary backend delays or network restrictions (VPN/proxy/firewall).
Wait 5–10 minutes and try again first, as the issue is often transient. If it persists, disable VPN/proxy and make sure you are using an LTS version of Mendix Studio Pro.
As a workaround, you can create a Blank App from the Mendix Portal and then open it using “Use Studio Pro”, adding required modules later.