This is tricky, OP. It's unfortunate that the main thing that is offputting for me is something you can't change - it's a really ugly block seemingly plonked down in a street full of more traditional houses. I would also say the 3rd bedroom is more of a boxroom rather than a useful bedroom.
However, in terms of things it is possible to change,if you want to, lots of people find it hard to imagine living in a space, so you have to paint a bit of a story for them. For example, I would make the balconies look more appealing by adding some plants; if you can hide the plastic bags on top of the wardrobe somewhere out of sight, that would be great; remove the exercise equipment and tidy up the desk in the box room; if you ever had a rug in the living room, put it back, as it looks a little too bare at the moment.
I'd also get the estate agent to correct the typos in the ad and state how long the lease is.
It's already a really clean, tidy flat OP; it may only be little tweaks here and there, and perhaps re-framing the content of the ad - it's very factual and doesn't exactly paint a positive picture. A lot of sites now have a message from the owners about what they loved about living there (a little cringe, I know, but still useful) or their descriptions are more generous e.g. it mentions the balconies but doesn't highlight how big they actually are (many people aren't good at visualising a space just from the numbers on a floor plan) or what they could be used for - the large terrace provides fantastic outdoor entertaining area plus abundent room for the green fingered to grow their own fruit and vegetables etc. (I'm not a wordsmith when it comes to selling houses, but you get the point.)
Also, what has the estate agent said about the lack of interest?