Can't figure this out

Puzzle refuses Rook to B4. Somebody help a befuddled geezer.

Could you post the puzzle in the comments or a link to the puzzle?

That would help.

I tried pasting a screenshot but it wouldn't take it. Maybe too big.

I just tried setting it up on the insert tab, got it all done, clicked insert, little gray board which disappeared when I clicked post. I don't seem to be very good at this.

Ah. There it is. I Hope.

I have posted the position with some sample lines below:

I hope this helps show why Rf2+ is the only correct answer.

Wow. Thank you very much. I am working on learning the game and find that one of my problems is not seeing. I looked at this and just didn't see f3. This helps me confirm that an erroneous puzzle is way more improbable than an erroneous me. 

That's good that you ask, I know I have learned a bit from more experienced people. 

Full disclosure. I'm 83 years old and using this sport to ward off dementia. Obviously I cannot tell if it's working (observer bias, you know), but it sure is taxing and I love it for that. I take a long time to analyze positions, partly age, partly inexperience no doubt, but it has to help to put in a couple of hours a day thinking stuff through. Thanks again.

Well, it might be working - you certainly don't sound like someone with dementia.

Remember there are 3 ways to get out of check:  (1) move the king, (2) capture the checking piece, and (3) interpose a piece.  That last method is commonly missed by beginners in the heat of the battle.  Indeed, that was the type of move that you missed, so don't feel bad about that.