Cuebiq holds no account, email or name for you, only your phone's mobile advertising identifier, so a request without it goes through and quietly matches nothing.
On Android open Settings, tap Google (listed on some phones as Google Services), open the All Services tab and tap Ads. Your Advertising ID is the long string at the bottom. Cuebiq's form tells Android users to go to Settings > Privacy > Advanced > Ads, a route from an older version of Android that current handsets don't have. The NAI's own device instructions, written against Android 16, give the same Google > All Services > Ads route.
On iPhone there's no route in Settings, and that's Apple's doing rather than Cuebiq's. Apple removed user-facing access to the IDFA, so the only way to read it is a third-party utility from the App Store, such as My Device ID by AppsFlyer or IDFA ATT, which report the value on screen. A utility only sees the real value once you switch on Allow Apps to Request to Track under Settings > Privacy & Security > Tracking and allow it when it asks. Otherwise Apple hands it zeros, which match nothing. That permission gives a third-party app the identifier and tracking access you're trying to take back, so as soon as you've copied the value, switch it off again, tell iOS to have apps you'd already allowed stop tracking, and delete the utility.
Copy the string somewhere before you continue. It's long, case-sensitive and worth pasting rather than retyping.