I haven't seen this "one time fee" in my previous bookings and would like to know what it is for.
Could it be the "service fee" which customers pay?
Owners: Beginning in September 2015, bookings by new account holders are charged a service fee amounting to 5-7% of the booking total.
Services booked through a Rover account created prior to the date the fee was implemented will not be subject to the owner service fee. The fee cannot exceed $25/booking ($35CAD/booking in Canada). It’s fully refundable should the booking be canceled by either the sitter or the owner prior to the first day of the service, in accordance with your sitter’s cancellation policy. If the booking dates change, the fee will be updated to reflect 5-7% of the new total.
https://support.rover.com/hc/en-us/ar...
If not, then I would contact Rover Customer Support at [Edit: Rover’s contact options have changed. Visit the Rover Help Center at https://support.rover.com/ to find the phone number, help articles, or chat with the team] to find out.