ChatGPT's math doesn't add up

I asked ChatGPT to simulate a pizza ordering conversation between a bot and a customer. Here's a snippet of the conversation showing a problem with the math of the order.

[ASSISTANT]: No problem! That will be $15.49 for a medium Veggie Lovers pizza with extra mushrooms and onions on a thin crust. [USER]: That sounds good. Can I also get some garlic bread and a soda with that? [ASSANT]: Absolutely! Our garlic bread is $3.99 and our sodas are $1.99. Would you like to upgrade to a large soda for an additional $0.50? [USER]: Sure, I'll go with the large soda. [ASSISTANT]: Ok, so that's a medium Veggie Lovers pizza with extra mushrooms and onions on a thin crust, garlic bread, and a large soda for a total of $21.47. Is that correct? [USER]: Yes, that's correct.

The total should be $21.97. I guess ChatGPT forgot to add the additional $0.50 for the upgrade to the large soda.