Kotlin Type mismatch, required: x found: x?

Short answer: Yes.

This means that the compiler is not sure if s.th. is !=null. If you are sure that it is not null you can also use:

val fragmentActivity = (iMainActivity as Fragment).activity!!

That gives you FragmentActivity instead of FragmentActivity? and you dont need the ?.let{}

Keep in mind that that might throw a NPE, while the

fragmentActivity?.let { fragment ->
   meViewModel = ViewModelProviders.of(fragment, vmf).get(MeViewModel::class.java) 
}

would simply not execute the block within .let{}, which is often less harmful then a NPE. See https://kotlinlang.org/docs/reference/null-safety.html for more.