WhatsApp error 131008: Required parameter is missing

Code 131008 means your request omitted a field the endpoint cannot work without. It is the WhatsApp messaging layer's version of a required-field validation error and it is always deterministic: the same payload will fail the same way every time until the field is added. The message string or error_data.details usually names the missing parameter.

On the /messages endpoint the fields most often missing are messaging_product (which must be the string whatsapp on every send), to, type, and the object matching that type, such as a text object with a body or a template object with name and language. On registration endpoints it is often the six-digit PIN. On media it is the file or the type.

This has nothing to do with permissions, rate limits, or the recipient. It is purely the shape of the request.

Like code 100, this is a synchronous, pre-queue rejection - nothing is billed and nothing arrives in webhooks. The request-shape walkthrough in the error-code guide shows a valid payload for each message type, and template payloads can be validated with the template checker before they reach the API.

Construct messages with typed builders that make required fields non-optional at compile or construction time, and validate against a per-type schema before sending. A contract test that sends each message type to a test number on every release will catch regressions in required fields before customers do.