Line a slow cooker with parchment paper, allowing the paper to extend up the sides for easy removal.
Add peanut butter, coconut oil, and sugar-free syrup to the slow cooker and stir to combine.
Cook on low for 2 hours, stirring every 30 minutes to ensure everything melts evenly and combines smoothly.
Stir in vanilla extract and sea salt, then pour the mixture into a parchment-lined 8x8 inch pan.
Sprinkle chocolate chips on top if desired, and refrigerate for at least 2 hours until firm before cutting into squares.