Diagnosis
That's the soundbar's protection circuit kicking in. It's almost always because the subwoofer and soundbar lost their wireless pairing.
How to Fix It
You need to re-pair them. First, unplug both the soundbar and the subwoofer from power. Wait a full minute. Plug the subwoofer back in first—you'll see its green light come on. Then, within 10 seconds, plug the soundbar back in. They should automatically search and re-link. The blinking red should stop and the soundbar will power up normally.
If That Didn't Work
Try moving the subwoofer much closer to the soundbar (like right next to it) and repeat the power cycle process. Thick walls or big metal objects can sometimes block the initial pairing signal.
Heads Up
If the red light is solid, not blinking, that means a different internal fault and you're probably looking at a service repair.