Season oxtail with salt, pepper, and 1 tbsp of ground allspice. Let marinate for 30 minutes if time allows.
Set Instant Pot to sauté mode. Add oil and brown oxtail pieces in batches. Remove and set aside.
In the same pot, sauté onions, garlic, and scotch bonnet pepper (if using) until fragrant, about 2-3 minutes.
Return oxtail to the pot. Add beef broth, soy sauce, browning sauce, remaining allspice, and thyme.
Close lid, set valve to sealing, and cook on high pressure for 45 minutes.
Allow natural release for 15 minutes, then carefully quick release remaining pressure.
Open lid, add butter beans, and simmer on sauté mode for 10 minutes to thicken sauce.
Adjust seasoning, garnish with green onions, and serve hot.