# `package.operation_invalid`

Provider operation holds what it can't, or lacks what it needs.

Area 11, [External services](../topics/external-services.md); not declinable; the next step is usually the agent's.

> A provider package's operations in `resources/` are each read and
> checked: its keys, `method:` and `path:` (each placeholder
> one of its input's fields, by its spelling on the wire), its `input:`
> one of the package's object types, its `failures:` the package's own,
> and `output_at:` and `failed_when:` places in the answer.

A placeholder in `path:` is filled from the input's field of that
spelling on the wire:






```jadpo
public resource parcels {
    get: {
        method: HttpMethod.get
        path: "/v1/parcels/{parcelId}"
        input: ParcelLookup
        output: Parcel
        changes: false
        source: PackageSource.written
    }
}
```

```text
error: `parcels.get`'s path names `{parcelId}`, which its input doesn't give
 --> shared/providers/acme_couriers/v1/resources/parcels.jadpo:4:15
  |
4 |         path: "/v1/parcels/{parcelId}"
  |               ^^^^^^^^^^^^^^^^^^^^^^^^ a placeholder with no field
  reason: A placeholder in `path:` is filled from the input's field of that spelling on the wire, and its input, `AcmeCouriers.ParcelLookup`, has no field sent as `parcelId`.
  next: Add a field `parcelId` to the input, or give the field the provider's spelling with `wire_name: "parcelId"` (agent)
  rule: package.operation_invalid
  help: https://jadpo.dev/docs/errors/package.operation_invalid

check failed: 1 error, 6 files
```