Want to call GetContactAttributes api from vxml based IVR application, Retrieves the contact attributes for the specified contact and we can make some decisions there in VXML based IVR application?

I assume you're integrating some legacy CC with Connect, more than likely fronting calls with Connect and the transferring them to your on prem CC. I've done something similar with Connect and Cisco UCCE and it works well. The right way and possibility the most scalable is to do a good bit of work up front. Setup a Cloudfront end point, that goes to an API gateway, which then hits an Lambda that makes the GetContactAttributes request to Connect. This also allows you the ability to consume this API from the agent desktop without any more work as well as potentially add more attributes from your other CC platform into Connect for more robust reporting.

david