Red light flashing means that the heater has overheated. That is usually caused by nothing more serious than a dirty filter. I suggest you turn off power to the spa, pull and clean the filter, and then put the filter back in place.
Next you will need to push the reset button on the heater, very firmly. No, it will not make an audible 'click,' and you may not feel it move.
Then turn on the breaker which runs only the pumps: I think it's the 30 amp breaker. It's easy enough to find out, turn on the one that makes the control panel start up and leave the other one off. This is so you can be sure the pumps are all primed and running before you turn on the heater. Run the jets for a few moments, then shut down to be sure you see the normal bubbles coming up from the floor from the ozonator.
Turn on the remaining circuit breaker now.
You should be good to go.