Why does ‘setting interrogation fail’? How can it be fixed ?

This is a message from your Carrier. Get in touch with them. This is not an iPhone issue.

Incorrect Date & Time: Ensure your iPhone's date and time settings are accurate. Go to Settings > General > Date & Time and verify they are correct.

Cellular Data Connectivity: Check if you have a stable cellular data connection or Wi-Fi connection (depending on the USSD code).

Network Settings: Try resetting your network settings. This will erase all saved Wi-Fi passwords and network configurations. Go to Settings > General > Reset > Reset Network Settings.

Did you make sure that in Settings/Phone/Call forwarding is enabled?

If it is, contact your carrier, since these services are all carrier related.

Also have a look at this related discussion:

Setting interrogation failed on iPhone - Apple Community