Where you pay
Plus is sold as Journal+, at £2.49 a month or £24.99 a year. Nothing is sold on chastity.report itself: paying happens on checkout.clackis.com, ClackID's billing for every app in the family, and you come back here when you are done.
Payment is taken by Stripe, and the charge shows as CLACKIS on your statement.
Changing or cancelling
In Settings, your Plus page has Manage your plan, which opens the billing page. Change how you pay or cancel there. A cancelled plan runs to the end of what was paid for, then Plus ends, and nothing you made is deleted.
If the billing page cannot be reached
Now and then the billing page cannot be reached. Nothing is charged when that happens. Try again in a minute.
Before you delete your journal
If you pay for Plus yourself, cancel it first: chastity.report will not delete your data while a plan you pay for would keep billing. Once it is cancelled you can delete straight away, without waiting for it to run out.