In case you have not added the Cognito libraries to your application, be sure to add them:

```yaml
 environment:
   sdk: ">=2.18.0 <4.0.0"

 dependencies:
   flutter:
     sdk: flutter

   amplify_flutter: ^1.0.0
   amplify_api: ^1.0.0
   # Be sure that this is added
   amplify_auth_cognito: ^1.0.0
```

Afterwards add the following code to your app before you configure Amplify:

```dart
await Amplify.addPlugins([
  AmplifyAuthCognito(), 
  AmplifyAPI(modelProvider: ModelProvider.instance),
]);
```