Add the oil to the insert and turn to sauté. Add the sausage and cook 7-8 minutes, or until browned. Use a slotted spoon to transfer the sausage to a paper towel lined plate. Set aside.
Add the onions to the pot insert and cook 5 minutes, or until softened. Stir in the garlic, celery, and green pepper. Season with cajun seasoning, salt, and pepper. Cook 5-6 minutes, or until the vegetables soften.
Add the beans, sage, and bay leaves. Add enough stock to cover the beans; stir to combine.
Place the lid on the pot and seal. Cook on high pressure for 40 minutes.
Allow the pressure to release naturally. Stir in the browned sausage, using the back of your spoon to gently mash some of the beans until they look creamy. Stir in the vinegar and green onions.
Serve the red beans with rice and top with hot sauce, as desired.