Hi @jkevens and welcome to our forum.
If the troubleshooting didn’t help (Litter-Robot III Open Air - Red Blinking Light) then probably cat sensor should be replaced.
It can be bought here: https://www.robotshop.com/en/litter-robot-3-open-air-cat-sensor.html
It can be replaced using this video: https://www.youtube.com/watch?v=wLwgz3hWgMg
If you bought it from RobotShop, please provide your order ID.