Please make sure that you are always using a candy/cooking thermometer in the formula the entire time you're feeding your bird, and you are never feeding him any formula at all that is colder than 104 degrees F, and no hotter than 110 degrees F. Even one degree cooler and he will develop a potentially fatal yeast/fungal infection, slow crop, or crop stasis, and even one degree higher any you'll burn his crop and cause a very bad wound and infection...
We get people who are hand-feeding unweaned babies on here all the time, and they very often become horribly sick, stop eating, start vomiting, etc., and it's usually because they were not measuring the temperature of the formula at all, they only "warmed the formula up", and 99% of the time it's well under 104 degrees F and far too cold to feed the baby, and the baby develops a horrible fungal infection and often dies, especially if you're in a country without many Avian Vets. This is not at all optional...
He looks very healthy, so that's good, but he also looks a bit on the older side of being unweaned...Do you know how old he is? Are you keeping pellets and a seed-mix in his cage at all times? You never want to "force-wean" him, it needs to be totally up to him when a formula feeding is removed or is a smaller amount. However, you do want him to start "abundance weaning" himself, and that means you need to keep pellets and seed-mix in his cage at all times...It is a very small cage for your bird (from the photos anyway, sometimes photos are deceiving, but it looks way too small), so you probably want to look for a much larger cage for him as already mentioned.
If you start to experience any issues hand-feeding him at all, or if he appears to be at all sick with symptoms such as becoming lethargic and sleeping more than usual/not moving/not playing as much, if he starts keeping himself fluffed-up all the time, any vomiting or watery stools, or stools with bubbles in them, or if he suddenly stops eating, then you need to find an Avian Vet immediately, because this is unfortunately very, very common when you buy an unweaned baby bird...