This is pending acceptance of my production API key access form submitted to Tremendous (https://www.tremendous.com/).
Pull Request: https://github.com/manifoldmarkets/manifold/pull/701
Market on same question with longer duration:
https://manifold.markets/jack/will-manifold-allow-mana-redemption-77bb8f85b270
As a reminder: scammers often ask for gift cards (e.g. Apple or Google Play or Steam) because they can be resold for cash on shady websites for a portion of their face value.
I would strongly recommend the Manifold folks not do the gift card thing: I would prefer that this website stay as a mostly-not-real-money prediction-based social network than it get attacked by the authorities.
I've done this myself, when I ended up with a US Play Store card I couldn't make use of; sold it for about 90% of face value on a website like https://gameflip.com/en/overview/sell/gift-cards/amazon (don't remember if that was the exact one).
Converting them to cash is mildly annoying and you'll lose a bunch of the value but not too difficult if you're not a fraudster and happy to do ID verification to a website that trades them.