Confirms the payment of a provider-backed order item, moving it from awaiting_provider_confirmation to redeemed. It takes no request body. Requires a producer access token for the application.

Only an item in awaiting_provider_confirmation can be redeemed. Any other state fails with 422 and an error_code. Built-in products (badge, multiplier, flair and coupon-code lines) settle at order time and have no manual steps, so they fail with 400 PRODUCT_NOT_ACTIONABLE. The response is the updated order item, in the same shape as Retrieve Order Item.