There are lots of ways that advertising could be tied to personal interests gleaned by having access to someone's ChatBot history. You wouldn't necessarily need to integrate advertisements into the ChatBot itself - just use it as a data gathering mechanism to learn more about the user so that you can sell that data and/or use it to serve targetted advertisements elsewhere.
I think a big commercial opportunity for ChatBots (as was originally intended for Siri, when Apple acquired it from SRI) is business referral fees - people ask for restaurant, hotel etc recommendations and/or bookings and providers pay for business generated this way.
Right, referral fees is pay-per-click advertising.
The obvious way to integrate advertising is for the LLM to have a tool to search an ad database and display the results. So if you do a commercial query the LLM goes off and searches for some relevant ads using everything it knows about you and the conversation, the ad search engine ranks and returns them, the LLM reads the ad copy and then picks a few before embedding them into the HTML with some special React tags. It can give its own opinion to push along people who are overwhelmed by choice. And then when the user clicks an ad the business pays for that click (referral fee).