Unable to Import Webview in custom Widget

I'm trying to use the webview package in my custom widget however I am unable to import it. I understand that this package already exists in flutterflow but I need to use the onMessageReceived function for some custom functionality.

Compilation Error in Custom Code
Launching lib/main.dart on Web Server in debug mode...
Waiting for connection from debug service on Web Server...
lib/custom_code/widgets/docu_seal_editor.dart:35:14: Error: The method 'WebView' isn't defined for the class '_DocuSealEditorState'.

import 'package:webview_flutter/webview_flutter.dart';

class DocuSealEditor extends StatefulWidget {
  const DocuSealEditor({
    Key? key,
    this.width,
    this.height,
  }) : super(key: key);

  final double? width;
  final double? height;

  @override
  _DocuSealEditorState createState() => _DocuSealEditorState();
}

class _DocuSealEditorState extends State<DocuSealEditor> {
  @override
  Widget build(BuildContext context) {
    return Container(
      width: widget.width,
      height: widget.height,
      child: WebView(
        initialUrl: 'about:blank',
        onWebViewCreated: (WebViewController webViewController) {
          webViewController.loadUrl(Uri.dataFromString(
                  '<html><body><p>This is a basic HTML page in WebView</p></body></html>',
                  mimeType: 'text/html',
                  encoding: Encoding.getByName('utf-8'))
              .toString());
        },
      ),
    );
  }
}