Could you please check the following:
1. Do you have VPN (Virtual Private Network) enabled?
2. Is your wifi router settings has client/wireless isolation enabled?
This setting prevents direct communication between connected devices/computers.
3. Please check on your iPad Settings -> Privacy -> Local Network, if spacedesk is on the list and enabled?
For assistance, please also check the Troubleshooting -> Network Connection chapter in the user manual https://www.spacedesk.net/user-manual/.