Preheat slow cooker on high with 1/2 cup water.
Pat dry the ribs with a paper towel.
Mix the 2 tbsp paprika, 1 tbsp mustard powder, 2 tsp cumin, 2 tsp salt, 1 tsp celery seeds, 1 tsp garlic powder, 1 tsp black pepper, and 1/4 cup sugar substitute in a small bowl.
Rub the spice mixture over the 2 lbs pork spare ribs.
Cook on high for 4 hours.
Line a baking sheet with aluminum foil.
Set oven to broil.
Broil the pork spare ribs for 5 minutes.
Flip the pork spare ribs.
Broil for an additional 5 minutes.