Hello @Jorge2801 ,
Since it is the Guest who is asking for a cleaning fee mid-stay, yes you may charge them an extra cleaning fee. The cleaning fee they paid during the booking process is supposed to be the payment for the cleaning services after they leave to prepare the listing for the next guest.
It is also advisable to put a disclosure on your house rule and/or listing description under "other things to note", an extra cleaning fee clause, which can either be optional or mandatory.
For example, you may write that short-term bookings (less than 28 days) have an optional mid-stay cleaning with a fee of $XX while long-term bookings (28 days or more) have a mandatory mid-stay cleaning of $XX every month.
This will inform your future guest and manage their expectations when it comes to cleaning the listing and its related fees.
All the best. 🙂