I don't know of any legal rulings or laws, which say not disclosing an embedded ad is illegal. In fact quite the opposite. There are loads and loads of prior such cases, movies, TV shows being an example.
For example every product mention (snapple, oh henry candy bars, jr mints) on Seinfeld was an ad. The skit is written, but any product can be dropped in. If no advertisers are interested, made up names are used.
This has been going on for 100+ years, including radio.
US and EU law already cover this: undisclosed paid promotion that looks like neutral content is generally illegal (FTC Act + Endorsement Guides in the US, UCPD + DSA in the EU). Product placement in old TV/film is the historical exception, not the rule. An interactive "assistant" secretly steering you because someone paid for it is legally much closer to a deceptive influencer ad than to a Snapple bottle in Seinfeld.
For example every product mention (snapple, oh henry candy bars, jr mints) on Seinfeld was an ad. The skit is written, but any product can be dropped in. If no advertisers are interested, made up names are used.
This has been going on for 100+ years, including radio.
Why would ChatGPT be special?