Help with unbalanced ending

I was white here, and eventually drew. (against 1800+, so that's good!)

I played a5. But, apparently, there's a winning line, according to SF. Can you see it?

It would've been nice if you would've put a puzzle instead of a diagram.

I'm looking for an idea, not a forced sequence

How about something like this?

1. Rb4 Nf5

2. Rc4 Kxh4

3. Rc7

Yeah, Stockfish likes 1 Rb4 Nf5

But after 2 Rc4 Ba6 seems to become very complicated, I really cant understand the lines. (Although apparently still winning)

SF suggests 2 a5, I really dont know why it's so much better than on the previous move

Well, you asked if we could find the winning line, so I was guessing that it could've been a puzzle.

I guess I should have phrased it better...

No "should" about it. Your meaning is quite clear, the title's a big clue.