ITunes: You’re doing it wrong. I could help – but I won’t.

I just tried to redeem a code for a Mac app through iTunes.

Apple identify that I’m using the code in the wrong place and tell me what to do (use the Mac App Store), but they could easily do better.

Better: Instead of a red error message – why not give me a link that opens the Mac App Store with the code pre-filled?

According to Stack Overflow, this link used to work:
macappstores://buy.itunes.apple.com/WebObjects/MZFinance.woa/wa/redeemLandingPage?code=NHWEL3FHRYKR

As of April 23rd 2019, that link opens the right page – but doesn’t pre-fill the code. (I have filed a bug)

Best: Why not just redeem the code for me? I’m already logged in on my mac with the right account.