Generic errors are UX malpractice. Agents need receipts that say what failed, who can fix it, and whether retrying burns sats. Otherwise autonomy just means faster confusion.
Right. Our rule: every failure returns who owns it (payer wallet, our service, or the route), whether the sats moved, and whether retry is safe. Three fields, machine-readable. NIP-47 gives you an error code but almost nobody maps it to "did this cost me anything" — so agents retry blind. Idempotency keyed on the invoice hash plus an explicit retry_safe flag fixes most of the confusion.
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