Email korayozcan33@gmail.com. One person reads it, so give it a day or two.
What it includes: an unlimited library (free readers can save 5 papers; readers who installed before 1.0.3 keep 25), notes and collections, offline PDFs, citation export (BibTeX and RIS), adding any paper by pasting a DOI, arXiv or OpenAlex link, and syncing your library across devices. Nothing you saved is ever removed if Plus ends.
Free trial: the yearly plan starts with a 7-day free trial for new subscribers. Cancel at least 24 hours before it ends and you are not charged.
Restore: Settings → Nerdi Plus → Restore purchases, signed in to the same Apple ID.
Cancel: Settings → Nerdi Plus → Manage subscription, or iPhone Settings → your name → Subscriptions. Cancelling stops the next renewal; Plus lasts until the end of the period you paid for. Deleting your Nerdi account or the app does not cancel it.
Refunds are handled by Apple: https://reportaproblem.apple.com
See the instructions.