Contact

Plinth is a one-person operation. Two addresses, depending on the topic:

Address	When to use
support@plinthprep.com	Refund requests, sign-in problems, question corrections, billing receipts, bug reports — anything user-facing.
admin@plinthprep.com	Legal notices, DMCA, privacy / data-subject requests, partnership and press inquiries, anything contractual.

Best path by topic

Topic	Where to send it
Question correction	support@plinthprep.com — include the question ID (visible on the result screen) and a short note on what's wrong.
Refund request	support@plinthprep.com — narrow exceptions only (duplicate billing, entitlement failure, mandated by law). All sales otherwise final; use the free preview to evaluate before buying. See the Refund Policy.
Billing / receipt	support@plinthprep.com — Stripe receipts also available from Settings.
Privacy / data request	admin@plinthprep.com — see the Privacy Policy for the full list of rights.
DMCA / copyright	admin@plinthprep.com — see the Terms of Service for the takedown procedure.
Press / partnership	admin@plinthprep.com — see also the press kit.
Bug report	support@plinthprep.com — include the browser, OS, and steps to reproduce. Screenshots help.

Typical response time: within 48 hours, often faster. If you're on a deadline (e.g., your exam is in a few days), say so in the subject and it'll be prioritized.