brake fault light flashing on display

[michael1]

for the last wk or so the brake warning light on the dash . the red round circle has flashed a few times and beeped away. only then to stop. nxt day may or may not do same. today it did it again and also got a warning message on dash display saying brake faul refer service manual or something like that. i just looked at brake fluid reservoir and ccant actually see any fluid if i take cap off because of filter. tried putting some in anyway and it does not seem to go in it remains in the filter area. i have shaken the car to look for movement of fluid but cant see any . any ideas anyone. does not appear to have any braking issues.