It’s 閉める + ~ておく (definition 9) in negative, 閉めておかない, but when you’re being casual, you can compress the ~てお~ to just ~と~. Not a typo, but perhaps a hair too casual for something that’s supposed to be illustrating vocab usage.
Good point Balthazar! I’ll bring this up to the team to see what they think!!
-Nick at WK
I vaguely remember being told that this form is uncommon in IRL Japanese (but it’s certainly very common in videogames and manga).
Update: the content team has changed this part of the sentence to: 閉めておかない. While it’s not a typo, they thought it may be worth changing it to something less casual so that learners at this stage can better understand it. Thanks for bringing it up!
Oh I totally missed that! Thank you so much! Good opportunity to revise the grammar lol