@Ray, Gyanendra Thank you for your question and interest in ACS.
We verified with the product group that ACS should work with Xamarin. @Rob Caplan - MSFT is correct in that the approach is to use the ACS .NET SDK within your Xamarin application. The exception to this real time functionality for chats will not work within Xamarin.
Unfortunately, there is no official documentation on using ACS within Xamarin at this time. We suggest you request this documentation on the Azure Feedback site, which the product group reviews frequently on items to address next. We will also share this feedback in our sync with the ACS product group later this week.
Please let us know if you have any further questions or concerns on this matter.