My fiddle leaf was doing brilliantly but now it’s leaves are all going brown. Any advice on how to fix much appreciated
Well thats a rather unwell looking Fiddle Leaf - but there are so many possible reasons it is not possible to be precise - us being remote. Seeing it close-up and personal is the only surefire way to diagnose the problem. However it looks to be systemic rather than external and curl grubs eating the roots is often a cause of slow encroaching death - and I'd say this plant is well on the way to that end. I'd suggest re-potting it and having a good look at the roots when you do it. Even a bit of root pruning might help stimulate some extra root growth. Before you put it back in the soil pop the bare roots into a dilute mix of Seaweed Tonic like Seasol. Re-plant it with fresh, premium potting mix and pour the rest of the mixture over the soil. This will at least give it a chance of survival.