Inkline is free to use: reading, the offline reader for up to 50 publications, notes, search, widgets and Voices, with no time limit. Inkline Pro adds monitors, watchwords, spoken briefings, analysis and unlimited publications, at £2.99 a month or £14.99 a year in the UK, each starting with a week free through the App Store. Billing is handled entirely by Apple; Inkline never sees payment details.
To cancel, open Settings on your iPhone, tap your name, then Subscriptions, then Inkline. Cancelling during the trial means you are not charged; cancelling later keeps access until the period ends.
Still stuck? Back to the help centre or use the contact route there.