Bonjour Stéphanie !

Here, the only valid answer is the singular "toute information supplémentaire", especially as in the audio, the liaison is clearly made between "toute" and "information" :) It's also the colloquial expression, as here "toute" is used as "any information".

I had a look through the exercise, and couldn't find anywhere where the plural version was displayed, do you remember where it might have occurred?

Cordialement