The main issue: You’ll need to transfer the title to fully sell your vehicle, but your lender possesses the title until your loan balance is satisfied. You’ll need to have their permission before you can transfer ownership of your vehicle.
Work with your lender to facilitate the sale: If you finance from a local institution or bank, then you can likely take the buyer to this location, have them pay you for the vehicle, and pay off the remaining loan amount all in a single visit. The buyer leaves with the vehicle and its title and you leave with some cash.
If your loan is provided by a larger lender with no local locations: You will likely need a temporary operating permit from the DMV or use an escrow service to allow the buyer to drive the vehicle until full ownership is transferred.