When blue LED blinks quickly, it means that the camera could not read the SD card normally so that it is unavailable to record. It may be caused by the card itself or the connection of it.
Firstly, please confirm that the used card.
Try to format the used SD card both via App and computer, or change another one to try.
It is recommended to use Samsung U3 SD cards for its better adaptation and durability.
And using the card cover for better connection.
Then, if formatting and changing cards could not solve the problem of recording, please check whether the card could be inserted well.
And try to poke the metal shrapnel signed by green for a better connection.
If the blue LED still blinks, please contact RunCam Customer Service to reflect problem, with offering clear photos of main board from both sides and invoice to confirm.