Reading state
Everything is on-chain: VaultUpdated for totals, Announcement for stealth payments, Shielded/Unshielded/SharesMoved for flows. Any standard RPC works.
Accepting payments
A merchant registers a meta-address, then scans announcements with its viewing key. The viewing key can live on a server without any spending power.
Running a relayer
Accept signed operations, check the fee covers gas at the current price, and submit. No permission needed.