Prepare the slow cooker by coating it with a light coating of cooking spray.
Season the chicken thighs with salt, pepper, garlic powder, and paprika on both sides.
Arrange the seasoned chicken thighs in the slow cooker in an even layer.
Pour the barbecue sauce over the chicken, ensuring all pieces are well-coated.
Cover the slow cooker with the lid and cook on low for 6–7 hours or high for 3–4 hours, until the chicken is tender and fully cooked.
Once cooked, remove the chicken thighs and set them aside on a serving platter.
Whisk the remaining sauce in the slow cooker until smooth, then pour it over the chicken.
Garnish with chopped parsley before serving.