Hello, BIrvin
Sorry to hear about the issue.
To fix it, please add the following declaration to your .h file:
void Prox_Implementation(AActor* OtherActor, UPrimitiveComponent* OtherComp, int32 OtherBodyIndex, bool bFromSweep, const FHitResult & SweepResult);
Then implement the function in your .cpp file.
Please note that for Blueprint Native Events, you should add the _Implementation function, which provides the default behavior (in case there is no Blueprint implementation available).
Hope this helped!
Have a great day!