For one thing, the Uber integration in Messenger was made possible because mobile payment mechanisms are now commonplace in chat apps. Since you can send money directly within Facebook Messenger, that payment vehicle can in turn be used to pay bots for products.
2016 will be the year of conversational commerce
Chris Messina

Great inventory of emerging opportunities as well as issues in conversational commerce, Chris. About payments, you’re right that Facebook Messenger and other chat apps do a good job of providing a payments mechanism. Another low-barrier-to-adoption way could be for the bot platforms like Telegram and to include payments API’s for the more ubiquitous mechanisms, e.g. Apple Pay, Paypal and Google Pay.

Rather than entering your credit card info in each chat app, an OS-level mechanism like Apple Pay could potentially be enabled across all interfaces including bots, apps, browser, wearables and any other user interface that could benefit from payments. Not to mention the fact that biometric authentication makes such *Pay’s some of the most secure payment mechanisms out there.