Talk to a person.
A public support address has not been published yet.
Rather than print a mailbox that nobody is reading, this page says so. If you already have an account, replying to any email Omnidara has sent you reaches us. Otherwise this page will carry a support address before launch.
Data protection requests
Two of your rights are built into the app and need no request: Settings → Your data downloads a copy of your data (the Privacy Policy lists what the file holds and what it leaves out), and Settings → Delete your account erases the account and its contents when you confirm it with your password, once no plan is still set to renew.
You can also correct what you entered yourself - your name, your listings and your listing defaults - where you entered it. For anything else, including a correction to a record you cannot edit, reply to any email Omnidara has sent you, as the top of this page says. Section 7 of the Privacy Policy says what each of these rights is.
The legal basis and retention periods are set out in the Privacy Policy and the Data Processing Agreement.
Billing
Plan changes, invoices, payment methods and cancellation are handled in the Stripe customer portal, reachable from Billing in the app.
Upgrades take effect immediately; downgrades take effect at your next renewal. The Terms say exactly what is charged and when.