It is likely that you have not properly formatted the SD card. Please note that CE models need to be formatted as FAT32 with an allocation size of either 16k, 32k or 64k to function properly. Formatting it as exFAT and/or setting the allocation size to 4k or 8k will not allow Fly12 CE to record video.
Note: It is important that you are using a recommended card. You may check the list of cards to consider from the link below.