Zapier MCP bills 2 tasks per success; retry Sume tools with one key

Zapier's MCP page says each successful call costs 2 tasks and failed calls do not count. It also gives the size of the catalog: 9,000+ apps and 40,000+ actions. Sume's side is different: a paid tool call that is accepted reserves wallet funds, and the safe way to retry is to send the same idempotency_key. The Sume docs do not describe a Zapier connection, so this post covers the two billing rules and how to retry safely, not a setup.

Two billing rules

The arithmetic

On Zapier, 5 successful calls cost 5 x 2 = 10 tasks, and 3 failed attempts before them add 0. One Sume generate_video call, retried twice with the same key after a transport error, creates one job and reserves one estimate. Retrying with a new key each time is the mistake that creates three jobs and three reservations.

Retrying a Sume tool safely

When a client times out, the job may already exist. The docs say not to submit the paid request again because a local worker timed out, and to reuse the same key for an exact retry. For an MCP wait, a slice that expires or a gateway error such as 524 on jobs_wait is a transport failure and not a job outcome: wait again on the same ids, or read jobs_status once.

Errors tell you what to do. 429 rate_limited means back off, and use retry-after when present. 429 queue_full means stop adding work. 503 provider_capacity_exceeded means retry later with the same key. 402 insufficient_credits is a balance problem and a retry will not help.

{
  "idempotency_key": "order-8823-clip-v1",
  "max_spend_usd": 2,
  "payload": {"prompt": "Slow push-in on a ceramic mug"}
}

A rule of thumb

• Derive the key from the business event (an order id plus a version), not from the clock.
• Change the key only when you change the payload on purpose.
• Add max_spend_usd for anything an automation fires without a human.
• Check Zapier's current task rules on its page before you cost a workflow.

Where retries come from

Retries can come from your client, your orchestration layer, or an agent that repeats a tool call. Set the idempotency_key in your wrapper from the business event, so every repeat of the same operation carries the same key.

If the second call has the same key and the same payload, Sume treats it as a retry. If the payload differs, the answer is 409 idempotency_conflict, which is a signal that something upstream changed its mind, not a transient error.