Create the dry rub- in a small bowl, stir together the brown sugar, oregano, chili powder, paprika, salt, onion powder, garlic powder and cayenne. Rub the ribs generously, front and back. If not using barbecue sauce, wrap the ribs in Saran Wrap and refrigerate for at least 2 hours, or overnight. 

Pour the beef broth, vinegar and liquid smoke into the insert of the Instant Pot, and set the rack inside. Fit the ribs inside the pot, then cover and set top valve to "seal." 

Set the machine to cook on the "Meat" setting for 40 minutes. When timer has run out, naturally release for 10 minutes, the quick release to finish. 

Preheat a grill to medium heat and lightly oil the grates. Carefully remove the cooked ribs from the Instant Pot, and place on grill. Baste with chosen barbecue sauce. After 3-4 minutes. turn the ribs over and repeat on the following side. I usually do this twice on each side. (Conversely, you could also use your oven's broiler for this step).

Remove from grill and serve.