Controller in Web GL doens't work

[RamiroNoronha]

Describe the bug
I am having a problem with the controller, when I am using Web GL. The onCreated method doesn't work, because when I try to send a message to unity, nothing happens.

To Reproduce
Steps to reproduce the behavior:

1. I do Flutter Export Web GL
2. I created the method to inicialize the controller
3. I put a print to see the controller
4. The message is Instance of 'WebUnityWidgetController', but doesn't work.

Expected behavior
Send a message to unity, for the unity opens the scene.

Screenshots

Unity (please complete the following information):

• OS: [e.g. iOS] Web
• Version [e.g. 22] Chrome
• Unity Version 2022.1.17f1

Additional context
Add any other context about the problem here.

[jesseburstrom]

I found the solution! In the created index.html file for unity under build/web/UnityLibrary you have to add
.then((unityInstance) => {mainUnityInstance = unityInstance}); on the createUnityInstance method alternatively write mainUnityInstance = await createUnityInstance(... before. Some cut/paste error logic in the build.cs in unity causes this!

[timbotimbo]

Did you use the latest unitypackage?
Sending messages seems to work fine when I build the example. (windows Unity 2022.1.23)

And it looks like code similar to your suggestion is already added by build.cs

flutter-unity-view-widget/example/unity/DemoApp/Assets/FlutterUnityIntegration/Editor/Build.cs

Lines 290 to 295 in 7f55bc2

	indexHtmlText = indexHtmlText.Replace("}).then((unityInstance) => {", @"
	}).then((unityInstance) => {
	window.parent.postMessage('unityReady', '*');
	mainUnityInstance = unityInstance;
	");
	File.WriteAllText(indexFile, indexHtmlText);

[UPDATE]
jesseburton's suggestion is resolved here.
I'm still not sure what the original issue here is. Either an outdated unitpackage, or a different index.html export for this version of Unity.