LNK2019 error when retrieving a TextureReference

I have a FPostProcessSettings variable called skyAmbientPPSettings and a APostProcessVolume* variable called SkyAmbientPostProccessVolume. Whenever I call the line of code below, I get the LNK2019 variable also shown below.

Code in question:

skyAmbientPPSettings.AmbientCubemap->TextureReference = SkyAmbientPostProccessVolume->Settings.AmbientCubemap->TextureReference;


error LNK2019: unresolved external
symbol “__declspec(dllimport) public:
class FTextureReference & __cdecl
FTextureReference const &)”
referenced in function “public: void
__cdecl ABrickSkySphere::Update(float)”

Does anyone know how to resolve this error?

Does anyone know what is causing this behavior?

For right now I am just going to use the code below. Please let me know if you have any other solutions or know the cause to the original problem.

skyAmbientPPSettings.AmbientCubemap = SkyAmbientPostProccessVolume->Settings.AmbientCubemap;