Hi! I have a question about formula

On Wednesday I started fortifying my breastmilk with 1/2 tsp of Similac neosure formula but last night for his two nights feeds I gave him full formula instead of breastmilk and today he’s been vomiting/spitting up its white im guessing curdled milk. Is he not liking this formula? Or am i over feeding him?

He was In the nicu for 49 days ) when they ran out of my breastmilk he was taking enfamil gentlease and he did fine with it.