Don't just build and forget
Conversational UI is a relatively new trend and it is also extremely dynamic. Whether supporting new types of devices and channels, adding new functionalities, or improving the UI and UX, the first version of chat and voice applications is just the beginning.
Learn from the client experience, track where your solution fails, and measure whether it offers any value at all to your clients. It is a continuous evolution. Remember, the greatest challenge of conversational UI is in many cases less the technical constraints and more the linguistic ones. Most importantly, allow your users to interact freely within a specific limited space, but also to expand the space that is automatically supported. If you start by offering five functionalities, see how you can expand that and offer more with each version you release.