This page provides troubleshooting help and answers to frequently asked
questions about using Firebase Local Emulator Suite. If you
can't find what you're looking for or need additional help, contact
[Firebase support](https://support.google.com/firebase/contact/support).

#### Why do Local Emulator Suite logs show an error starting with
"Multiple projectIds are not recommended in single project mode"?


This message means the Local Emulator Suite has detected it may be
running a particular product emulator using different project IDs. This may
indicate a misconfiguration, and can cause issues when emulators try to
communicate with one another, and when you try to interact with emulators
from your code. If project IDs don't match, it often appears that data is
missing, because data stored in emulators is keyed to projectID, and
interoperability depends on matching project IDs.


This has been a common source of confusion among developers, so by
default the Local Emulator Suite will only allow running with a
single project ID, unless you specify otherwise in the
`firebase.json` configuration file. If an emulator detects more
than one project ID, it will log a warning and potentially throw a fatal
error.

Check your project ID declarations for mismatches in:

- **The default project set at the command line.** By default, the project ID will be taken on startup from the project selected with `firebase init` or `firebase use`. To view the list of projects (and see which one is selected) use `firebase projects:list`.
- **Unit tests.** The project ID is often specified in calls to the Rules Unit Testing library methods `initializeTestEnvironment` or `initializeTestApp`. Other testing code may initialize with `initializeApp(config)`.
- **The command line `--project` flag.** Passing the Firebase CLI `--project` flag overrides the default project. You'll need to ensure the value of the flag matches the project ID in unit tests and app initialization.

Platform-specific places to check:

|---|---|
| **Web** | The `projectId` property in your JavaScript `firebaseConfig` object, used in `initializeApp`. |
| **Android** | The `project_id` property inside the `google-services.json` configuration file. |
| **Apple platforms** | The `PROJECT_ID` property in the `GoogleService-Info.plist` configuration file. |


To disable single project mode, update `firebase.json` with the
`singleProjectMode` key:

```
{
  "firestore": {
    ...
  },
  "functions": {
    ...
  },
  "hosting": {
    ...
  },
  "emulators": {
    "singleProjectMode": false,
    "auth": {
      "port": 9099
    },
    "functions": {
      "port": 5001
    },
    ...
  }
}
```