Sume job metadata on Kling motion control and H3 Max lip sync

Yes. Kling 3.0 Motion Control and MiniMax H3 Max Lip Sync both accept an optional metadata object. Sume's schema says it is 'stored with the Sume job request' and 'not sent to the provider', so it is a place for your own labels, not a way to pass settings to the model.

What does metadata accept?

An object with additionalProperties: true, so any JSON keys. The text is the same on both routes. Nothing in it reaches the provider, so putting a prompt or a style flag there changes nothing about the clip.

The schema does not say which read returns it, so submit one test job and look at the job you get back before building on it.

What should I put in it?

Your own ids: an order number, a campaign tag, the scene name. Do not put secrets or personal data in it; it is stored with the request.

For retries, the stronger tool is Idempotency-Key: reusing the key with the same payload returns the original job with idempotency_hit: true, and the key is returned on every job object, so it doubles as a join label.

Can metadata stop a double charge?

No. Metadata is a label. Only the idempotency key makes a retry adopt the first job instead of paying twice. Jobs and results says retrying the submit with the same key is fine, and submitting a new paid job for the same intent is not.

Send both: a stable Idempotency-Key per intended clip, and metadata that names the clip in your own system.