First off thanks for putting in the time on this plugin :)

I noticed today that the styleString parameter doesn't work on iOS. I'm using a custom style (built in Mapbox Studio), and I pass the mapbox:// URL for it to styleString. On Android it works fine, and the style is applied as expected. On iOS however it has no effect.

I think I have tracked down the problem to this class, which filters out all custom style URLs. I'm not familiar enough with Mapbox on iOS to know if this is by design though, or I would have raised a PR for a fix.