Free lesson~8 minFresh · 2026-07-22 Path: Build your first x402 service

Idempotency: never pay twice for one unlock

Slow unlocks are not unpaid unlocks. Design attempt ledgers so agents do not double-transfer.

Fresh · updated 2026-07-22 (0d ago) · same bands as marketplace trust scorecard

This lesson is free and complete. You do not need to buy a skill to understand the material.

The scary failure

Agent pays → network lags → agent thinks it failed → pays again → two transfers, one product.

**txHash is the redeem key.** Retry unlock with the same hash. Do not broadcast a new transfer unless the first is known failed/dropped.

intent_id

skill_id

challenge snapshot

txHash (once broadcast)

unlock_status

Only if:

Prior tx reverted / never broadcast, or

Merchant explicitly says that tx is invalid for this skill

Idempotency is product safety for agent wallets.

Skip this section if you are only learning. Sealed packs implement ideas — they are not the lesson.