In order to spy on iPhone/iPad no jailbreak with iKeyMonitor, you need to ensure 2-factor authentication is turned off on the target device. You can open web browser from a computer or a cellphone, log into applied.apple.com and disable two-factor authentication.
1. Sign in to appleid.apple.com
Go to the “Security” section. Then click “Edit” if you are using computer browser.
2. Tap on "Turn Off Two-Factor Authentication" and select "Continue" when asked.
3. Create new security questions, and 2-factor authentication will be turned off.
If the iCloud account is created in iOS 10.3 and later, probably there is no option to turn off two-factor authentication on your Apple ID account page, which means you can't turn it off by yourself.
In such a case, we suggest that you contact Apple support and ask them to disable two-factor authentication for you.