How would I go about getting this working with C# mono

[Pa1yn-dev]

If someone could give me pointers it'd be much appreciated!

[CedNaru]

This a C++ plugin. You can't directly use it from C#, only GDScript can.
Indirectly, you could use it from C# the same way you would call GDScript from C#, which is very cumbersome to do:
Calling GDScript from C#

[Pa1yn-dev]

I mean to utilise unity's integration which uses C#, instead to use godot. Worst case scenario calling GDScript from C# could work.

[CedNaru]

I don't understand. The unity plugin for FMOD won't work in Godot obviously. And if you are asking about FMOD itself, we are using the C++ api, not the C# one.