デベロッパの回答 、 Hey, thanks for reaching out. Please note that the discount offers are limited in time. It might be that it was just over unfortunately :( Besides that, you can always request a refund or clarify this issue with Apple, as all financial operations are made directly between the user and Apple App Store.
Hope, you will find it useful, and can share if the issue is solved.
Best regards, Support Team
Just make it a paid app I hate downloading apps that are supposedly free only to find out you need a monthly subscription. If you’re to cheap to pay the apple store fees just sell your app elsewhere. I don’t think apple likes what you’re doing either.