Which payment types are available is decided by your app store and your country: card, direct debit, PayPal, balance or carrier billing, depending on the store. Citily itself never receives payment details and stores none.
Android: Play Store → profile picture → Payments & subscriptions → Payment methods. There you can add a method or change the one stored for Citily.
iPhone: Settings → your name → Payment & Shipping.
The charge failed. Your store will tell you and will normally try again; until the payment goes through, access can pause. Store a valid payment method, and the store restores the subscription by itself.