Service fee changed randomly

[Clare676]

I'm looking for some assistance please to understand what and why this has happened. Still new with air BnB. All my bookings that have come through, I have paid 15.5 and now on a new reservation we are on the 3% split fee. Why has this happened? Should I amend my cost per night so guest aren't paying too high, or will it revert back or is this a setting I can change? Any help welcome. 

[Clare676]

Also or changed our nightly rate when we looked at the fee by £20 less paid by the guest! Confused.com