Without knowing more this will be difficult to diagnose. First step is to factory reset the device, have you tried that yet? Also power cycle your router and phone.
Hello, Is the a new cameras? Or is this an old camera that has stopped working? Did you change your wifi setup in any way? Here are the instruction to reset it to FACTORY DEFAULT. But before you do make sure you REMOVE the camera from the app.
Make sure you do a factory reset and not just a restart
