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**Meaning**

If the script is using any of the [advanced services](https://developers.google.com/apps-script/guides/services/advanced), they must be enabled first. If the service is not enabled, it will not be added to the global scope (as a value of a global variable), resulting in an instance of `ReferenceError` being thrown (as the script is referencing a non-existent variable). 

**Reproducing**

To get a reference error when calling a method on an advanced service, declare and run the following function in a new script or one that does not have the [Advanced Drive Service](https://developers.google.com/apps-script/advanced/drive) enabled:

```typescript
const driveServiceIsNotDefined = () => {
  try {
    Drive.Files.list({ q: "" })
  } catch(e) {
    console.log(e)
  }
}
```

**Fixing**

If you are using Google's online IDE, since the overhaul of it, simply open the "Editor" tab from the left sidebar, click on the "Add a service" button under the "Services" section, and then choose the appropriate service.

Note that the modal allows you to override the _identifier_ of the service to a name of your liking (the default name matches how Google's documentation references the service). If you change it, the script will have to reference that identifier instead of the service name.

> Historical aside: in the old IDE, one needed to go to "Resources -> Advanced Google Services" menu and enable the referenced service there (the identifier could be overridden too).

If you are developing locally and using [CLASP](https://github.com/google/clasp) to push the source code to the project, you will have to explicitly specify the advanced services used in the [manifest file](https://developers.google.com/apps-script/concepts/manifests). In fact, this is what is done under the hood when you enable the service in the GUI.

In the manifest, advanced services are specified under the `dependencies` field in the `enabledAdvancedServices` (which is a JSON array of service definitions), for example (enabling the Advanced Drive Service):

```typescript
"dependencies": {
    "enabledAdvancedServices": [
      {
        "userSymbol": "Drive", // identifier to reference
        "version": "v2", // version of the service to use
        "serviceId": "drive" // Google's service identifier
      }
    ]
}
```