[amp-story-interactive-binary-poll]: Dynamic behavior about a value of endpoint attribute

We have used two endpoint urls shared by amp.dev examples.
1. Endpoint value = [https://webstoriesinteractivity-beta.web.app/api/v1/](https://webstoriesinteractivity-beta.web.app/api/v1/)
Story URL = [Sample Example1](https://myampstories.visualstories.com/test-poll)
2. Endpoint value = [https://amp.dev/documentation/examples/components/amp-story-interactive-poll/results](https://amp.dev/documentation/examples/components/amp-story-interactive-poll/results)
Story URl = [Sample Example2](http://vs-subdomain.azurewebsites.net/myampstories.visualstories.com/testpoll)

For above Example1: The same output of % results is getting shown to any user for respective options. for eg. The percentages for Option1 looks same from end of no. of users even for same selection. The results are not dynamic.
For alternate, we have used another endpoint (in story Example2). The results are dynamic, but not sure about it's working as expected or not!

Please let us know which endpoint is correct to use? Is there any update yet to come as mentioned here: [README.md](https://github.com/ampproject/amphtml/tree/main/extensions/amp-story-interactive#backend-api)

Currently we are not using own backend as value for endpoint. Instead, is there a way, we can achieve this? Kindly do guide or suggest.

/cc @abhiz10 @shivkumardesigner @akashshah3991