Remove the membrane from the back of the ribs and cut each rack of ribs in half or thirds so that they fit easily in the slow cooker.
In a small bowl, whisk together the paprika, brown sugar, garlic powder, onion powder, salt, pepper, and parsley.
Sprinkle the dry rub over each side of the ribs and use your hands to press it into the meat.
Add the apple cider to the bottom of a slow cooker and place the ribs in the slow cooker.
Cook, covered, on high for 4 hours or low for 8 hours.
When ribs are very tender, but not quite falling apart, carefully remove them from the slow cooker to a large baking sheet. Brush with barbecue sauce.
Place under the broiler until the sauce has thickened and begun to caramelize, about 5 minutes. Keep a close eye as the sugar in the sauce can burn quickly.
Serve immediately.