Registry vs registrar
A registry operates a TLD (e.g. Verisign runs .com); a registrar sells domain registrations to end-users. End-users buy from registrars; registrars settle with registries.
The chain
ICANN delegates a TLD to a registry; the registry signs agreements with accredited registrars; registrars are the customer-facing storefront end-users see.
Why it matters
Registry policies (like .ai’s local presence requirement) override registrar UX — even if a registrar lets you buy without a local address, the registry may reject the registration.