Below are some factors that would caused to this problem, would you please try below tips and let me know if that work?
1. Full charge the drone and change the battery of the remote.
2. Make sure the wire of the camera is pressed inside tightly.
The light of camera will turn to red which means the wifi signal can be sent successfully to your drone, then you can reopen the WiFi signal to connect again.
3. Signal disruption ( Many wifi surrounded)
Would you please change to another place where there is less than 3 WiFi signals to try again?
4. Change to another phone.
5. If WiFi connected, no valid network and also no image from the camera, please refer to the video below for more assistance:
6. Would you please check if the drone can work well with the remote?