error CS0006: Metadata file `/home/dom/Projects/TurnBased/Library/ScriptAssemblies' could not be found

Similar to t$$anonymous$$s question, I am trying to get the dll location configured so my ale plugin can find correct DLL's to pick up symbols.

Currently I have the following configuration:

let g:ale_cs_mcsc_assemblies = [ \ expand('/home/dom/src/UnityInstalls/Unity-2019.4.0f1/Editor/Data/Managed/UnityEngine.dll'), \ expand('/home/dom/Projects/TurnBased/Library/ScriptAssemblies') ]

but t$$anonymous$$s is giving error CS0006: Metadata file `/home/dom/Projects/TurnBased/Library/ScriptAssemblies' could not be found
Does anyone know the correct configuration here