On this device we store timer state, a random analytics id, and any campaign tags from the link you used (source, medium, campaign). After you buy, a signed cookie marks Fifteen Plus on this browser. That cookie is not used to track you across other sites.
If you check out, Stripe receives your email and payment details. We do not store card numbers. We use your email only to restore a purchase on another device.
Product analytics (session started, upgrade viewed, checkout started, purchase completed) go to PostHog so we can see whether the app is useful and whether paid traffic pays back. We do not sell this data.
Questions: use the email on your Stripe receipt, or the support address in Stripe's public business details for next15minutes.com.