How to get an interface to return a pointer

Mostly got my interface except for the parts that are referencing pointers to Actors or UserWidgets.

For example:

UFUNCTION(BlueprintCallable, BlueprintImplementableEvent)
UUserWidget* GetUnitCard();

This just throws an unresolved external symbol. I’ve been googling for quite a while, but almost everyone who takes the time to talk about interface functions only ever talks about returning things like bools and fstrings (which I have working just fine) but not a pointer. I’ve also got functions which use a UUserwidget as an input variable and those are also throwing errors.