Hi Lorena,
I would suggest you go through all the basic checks and troubleshooting steps as it will solve most of the issues that can be encountered if properly followed. In the basic checklist first step is to ensure if your device is compatible or not. The DJI smart controller is not officially supported/tested by the Pix4Dcapture app. For more information, I would recommend you to go through our support article on Supported drones, cameras and controllers.
However, the DJI smart controller runs on the android version, so it might work. I have seen other users being able to plan a mission using the smart controller. I would suggest you to go through our community post on New DJI Smart Controller, which might be helpful to you.
Best,