Depending on how many ounces of breast fed milk your LO drinks you should add the correct amount of formula to your breast milk to get them use to formula
How much formula are you giving? Are you pace feeding it? Formula is soooo rough on their tummies so as April has said the slower the better x
If this is the first time, I’d try again and see what happens. My first born puked formula up every time I tried (@8 months old) and we found that he had a cows milk protein allergy, we tried all formula, even goat milk which is meant to be more gentle on the tummy and he puked every time. Our health visitors encouraged me to keep trying all different shop bought milks for a month before the GP have the diagnosis, which cost a lot of money on once used formulas. I wish we had just gotten the hydrolysed milk from the gp with the protein removed sooner.
Very slooooowly its toooo heavy for breastfeed babies