In a large bowl, combine oxtails, onions, scallions, garlic, thyme, red pepper flakes or scotch bonnet, hot paprika, bay leaves, soy sauce, pimento seeds, ketchup, and Worcestershire sauce. Mix well and marinate for at least 4 hours or overnight in the refrigerator, stirring occasionally.

Remove the oxtails from the marinade, reserving the marinade mixture.

Heat oil in a large heavy pot over medium-high heat. Brown the oxtails on all sides until nicely caramelized. Work in batches if necessary to avoid overcrowding. Transfer browned oxtails to the slow cooker.

Pour in enough beef broth to slightly cover the oxtails. Add the reserved marinade, chopped tomatoes, and carrots.

Cover and cook on high for 7–8 hours, or until the meat becomes tender and begins to fall off the bone. Check hourly to ensure the oxtails remain slightly covered with liquid.

At about 6 hours, add the drained butter beans and tomato paste. Add more broth or water if needed. Continue cooking uncovered for 1 more hour, skimming excess fat from the top and stirring occasionally.

During the last 30 minutes, season with salt and freshly ground black pepper to taste.

Remove bay leaves before serving. Serve Slow Cooker Oxtail and Butter Beans hot with rice and peas.