...Also, my U2 LOVES sweedish fish (little red gummy candy). She gets them every once in a while, but not too often as they are pure sugar. My macaw isn't in to sweets. She really likes fish and chicken. You might try some kind of protein, if you've already tried the usual treats (seeds, etc.).
Every parrot guardian uses different things based upon what your bird likes. Rosie would stand upside down for a small piece of cheese or a fishie cracker. Both in moderation of course.