[Grammar] If you have any question, please feel free to interrupt me at any time - mistake

[tom3m]

I was just curious and looked at the lesson plans on UE.com. And in the topic called presentation, there was an exercise to do with students. This sentence was marked as an appropriate to use when doing a presentation. My question is: Where's the mistake? The only things that comes to my mind is to change 'question' to 'questions' after 'any'. Is it just this?

If you have any question, please feel free to interrupt me at any time.

 

[Chicken Sandwich]

NOT A TEACHER

If you have any questions, please feel free to interrupt me at any time.

That's the only mistake I can find.