Integrate with custom widget chat

Hello we have a custom widget develop by our team, we want to integrate with zendesk chat.

We know that zopim chat and web-sdk chat are premade widget to implement in website, but we want to keep the experience of chat inside our widget.

We have a backend in java, so we tried the SDK:

https://developer.zendesk.com/documentation/classic-web-widget-sdks/unified-sdk/android/getting_started/#initialize-the-sdk

we tried to implement without success, because in this case it would be specific to android, correct?

is there any solution that could suit us?

Thanks.