storageRef.child is not a function in firebase

Having issues uploading files to Firebase using the react-firebase-file-uploader package.

The error received is Uncaught (in promise) TypeError: storageRef.child is not a function

Firstly, firebase is imported into my GatsbyJS Layout.js in componentDidMount as

Layout.js

componentDidMount() {
  const app = import('firebase/app');
  const auth = import('firebase/auth');
  const database = import('firebase/firestore');
  const storage = import('firebase/storage');

  Promise.all([app, auth, database, storage]).then(values => {
    const firebase = getFirebase(values[0]);
    !this.isCancelled && this.setState({ firebase });
  });
}

Then, firebase is added as props using React.createContext to pass functions to components as

FirebaseContext.js

const FirebaseContext = React.createContext(null);
export const withFirebase = Component => props => (
  <FirebaseContext.Consumer>
    {firebase => <Component {...props} firebase={firebase} />}
  </FirebaseContext.Consumer>
);

export default FirebaseContext;

Inside the firebase component, we use onboardStorage as a function containing this.storage as

Firebase.js

class Firebase {
  constructor(app) {
    app.initializeApp(config);

    /* Firebase APIs */
    this.app = app;
    this.storage = app.storage();

  // *** Storage API ***
  onboardStorage = () => this.storage;
}

let firebase;

function getFirebase(app, auth, database, storage) {
  if (!firebase) {
    firebase = new Firebase(app, auth, database, storage);
  }

  return firebase;
}

export default getFirebase;

Which is then passed to the FileUploader component in my form component as

Form.js

<FileUploader
  accept="image/*"
  name="avatar"
  filename="operator_accreditation"
  storageRef={() => firebase.onboardStorage().ref(`${uid}/files`)}
  onUploadStart={this.handleUploadStart}
  onUploadError={this.handleUploadError}
  onUploadSuccess={this.handleUploadSuccess}
  onProgress={this.handleProgress}
/>

each of the handle functions in Form.js are as follows

    handleUploadStart = () =>
    this.setState({
      operatorAccreditationIsUploading: true,
      operatorAccreditationProgress: 0
    });

  handleProgress = operatorAccreditationProgress =>
    this.setState({ operatorAccreditationProgress });

  handleUploadError = error => {
    this.setState({ operatorAccreditationIsUploading: false });
    console.error(error);
  };

  handleUploadSuccess = filename => {
    const { firebase, uid } = this.props;
    this.setState({
      operatorAccreditation: filename,
      operatorAccreditationProgress: 100,
      operatorAccreditationIsUploading: false
    });
    const storageOperatorAccreditation = firebase.onboardStorage();
    storageOperatorAccreditation
      .ref(`${uid}/files`)
      .child(filename)
      .getDownloadURL()
      .then(url => this.setState({ operatorAccreditation: url }));
  };

const uid is the the auth.uid

Adding a console message indicates that none are triggered on uploading a file.

The error occurs after a file is selected, indicating that the issue is at the storageRef of the FileUploader. What have I done wrong to get Uncaught (in promise) TypeError: storageRef.child is not a function?