Well, I tell you, as long as you free-feed protein, he will get full on it and reject anything healthier [nature hard-wired them for this because herbivores don't find abundant sources of high protein in the wild]. Sun conures are mainly fruit eaters in the wild [all conures are] and require a diet with low protein so free-feeding pellets, seeds, nuts, nutriberries, avicakes or anything else that is high in protein is not good for them. It not only makes them hormonal [read: aggressive], it also destroys their liver and kidneys in time.
All my parrots eat gloop and raw produce for breakfast and a seed or a nut/seed mix for dinner [it depends on the species] but it's always a small and measured portion [for a sun conure it would be a measuring tablespoon of a cockatiel mix and a nut during the summer and a budgie mix with half a nut during the winter]. They are not big on veggies although they do LOVE corn on the cob, carrots, sweet potatoes and sweet squashes] but they eat the ones in the gloop and love their fruit -leafy greens not so much. The trick is to feed them low protein all day long, to give them the raw produce early in the morning and before the gloop [because this is when they are hungriest and more willing to try new things] and to eat with them [not your food but his]. It takes a while but if you do it every single day and stick to it, he will start to eat it [especially if you eat it in front of him and pretend not to want to give him any
]. Mine get their cages uncovered and the blinds open at 6:15 am this time of the year. They get their raw produce at around 7 to 7:30 and their gloop at 8 to 8:30 [it depends on the brightness of the day] which is when the overhead full spectrum lights are turned on. In the afternoon, at around 3 pm, the lights [and the radio I leave on for them] are turned off and at around 4 to 4:15 pm they get their dinner and cages are covered at around 6 pm.