You need to add “ACollidingPawn::” in between “void” and “DebugStartGrowing” like so (in your .cpp):
void ACollidingPawn::DebugStartGrowing(){
UE_LOG(LogTemp, Warning, TEXT("Pressed!!!"));
}
Same is true for the second function “DebugStopGrowing”. It is also missing the “ACollidingPawn::” prefix.
And make sure that the two functions are properly defined in your .h file too.