Here are the most likely causes:
Data plan - Confirm that your plan is active (green) in your command center
Batteries - Try replacing your battery pack / batteries.
Connectivity Reset - Turn your data plan to Canceled for between four and five minutes, then turn it back to your desired plan. Sometimes reinitiating a cellular connection can jump start your camera. This is an easy one to do remotely, possibly saving you a trip to your camera.
Settings - Reduce Send Pic Resolution to Low and set a timelapse of 6-hours.
SD Card - Occasionally SD cards must be reformatted. For Y2 cameras, you can do this from your app. (For previous camera models, you'll need to visit the camera for this. Slide the camera to SETUP mode, press the Up arrow, then the MENU button. Then navigate so that format is red, press OK, then confirm. After this is complete, press the up arrow.)
Contact us for help! We know how frustrating this can be, you can always contact our support team and we can help.