DIAGNOSIS This usually means you don't have an active Arlo Secure subscription plan for that camera. Without a plan, you only get live view and motion thumbnails—no cloud recording.
FIX You need to subscribe or assign a plan. In the Arlo app, tap on the three-line menu, then go to Subscriptions. If you have a trial, make sure it's activated and applied to this camera. If you're setting up a paid plan, you need to add the camera to the plan's device list.
IF THAT DIDN'T WORK Check your library settings. Tap on a motion event thumbnail. If it tries to play but fails, your Wi-Fi connection might be too slow to stream the recorded clip. Test your internet speed. Also, verify that 'Record Video' is toggled ON in the camera's Motion Settings for the mode you're in (e.g., 'Armed').
HEADS UP Even with a subscription, there's a cooldown period between recordings called the 'Retrigger Time.' If motion is constant, it may only record the first event and then wait. You can adjust this in Motion Settings, but shorter times will drain the battery faster.