Optional OData filter expression used to narrow the returned webhooks. Filtering is supported on the webhook fields (id, name, endpoint, authMechanism, type, generation, createdAt, updatedAt, messageFormat) using the comparison operators eq, ne, gt, ge, lt and le, the logical operators and, or and not, the lambda operators any and all, and the boolean string functions startswith, endswith and contains. A malformed or non-predicate filter expression returns HTTP 400.