Dynamic values in text box

I just found the cause of the issue, I'm posting it for anyone else reading this thread.

Adding dynamic values on Smart Narratives visuals (and in text boxes) uses the Q&A feature under the hood. So I tried to add a Q&A visual and I got an error message saying that Q&A was not supported for this report.

The problem was that the language was configured as Spanish, even though I had the Spanish language support for Q&A preview feature turned off (I might have turned it on sometime in the past but then turned it off again, but apparently the model language was stuck as Spanish). Once I changed the model language back to English everything started working smoothly.