It’s late, but to those who are going on a journey.
The second parameter is the name of the component you want to attach.
For example, in my case, I wanted to attach it to the mesh component of the weapon I was creating.
FName PropertyName = *SpawnedProjectile->GetWeaponMeshComponent()->GetName();
FName SocketName = TEXT(AttachEndSocket);
GetCableComponent()->SetAttachEndTo(SpawnedProjectile, PropertyName, SocketName);
I tried debugging GetDefaultSceneRootVariableName() and nothing worked because it only returned “DefaultSceneRoot”.
So, I took the name of MeshComponent and since it is a String, I converted it to FName and applied it.