Contact.
One address for everything: [email protected]. It reaches the person who built the tool.
Billing and refunds
Plan changes, card updates and cancellation are self-service from your account page, through Stripe. A full refund inside the first 14 days, with fewer than 10 designs used, is a request from the same page, answered within a day. Anything else, write.
A design that came out wrong
A failed design refunds its credit on its own. If a design finished but missed what you asked for, send the design page link and what you expected; that is how the tool gets better.
Ideas and everything else
A tool you wish existed, a style you want added, a room type that is missing: write. The catalog grows from exactly these emails.