A1396 ipad could not be activated because the activation server is temporarily un

Solution 1:

Inability for an iPad to connect to the activation server could arise from a myriad of vectors depending on the state of the equipment and network you are utilizing.

Best practice is to ensure that the operating system and version of iTunes you are utilizing is up-to-date to resolve any latent compatibility issues.

Update macOS on Mac - https://support.apple.com/en-us/HT201541

Update to the latest version of iTunes - https://support.apple.com/en-us/HT201352

Should that not resolve your issue you can examine the relevant documentation here; albeit listed for the iPhone it should still be relevant for the iPad.

If you can't activate your iPhone - https://support.apple.com/en-us/HT201407

Is the activation attempting over a WiFi or a Cellular network? Should issues occur on a WiFi network, network configuration could be preventing such at which point it would be prudent attempt the same from a network provider elsewhere.

Apple Support has a handy iOS / iPadOS application that is useful for you to contact or schedule a call with them directly, who can then render potentially render further assistance.

https://apps.apple.com/us/app/apple-support/id1130498044