Plugged my scanner in and no codes,
Brake fluid is at the perfect level, running and not running, all pads are new. Still shows red warning and "low brake fluid" message.
Please help anyone who has had this problem, it’s driving me nuts…

I'm not 100% sure, but I think that the brake fluid level sensor is just a float switch in the cap, so perhaps it's that float or its contacts that are failing somehow.

What happens if you remove the cap, and hold it upside down?

It it is the cap/sensor that is faulty, it's about £40 (in the UK) for a new one.