# X_WEBHOOK_EVENT_INVALID

## Means

the event cannot be signed as declared

## Typical cause

an id or a topic that would make the canonical string ambiguous: outside 1–200 characters, or carrying a `:` or a control character. Refused BEFORE the mac is taken, because a mac over an ambiguous string is a valid signature for a delivery the sender did not write — over `v1:<t>:<id>:<topic>:<body>`, id `evt:01HZ` with topic `orders.paid` and id `evt` with topic `01HZ:orders.paid` are the same bytes

## Fix

change how your app mints the field `cause` names — the separator can never appear in either, so the edit is at the mint site and not at the send

[Outbound webhooks](/error-codes#outbound-webhooks)