Of course, as with everything with babies, there is no easy answer! It could certainly be reflux, since that commonly causes fussy eating. If this is the case, one thing they suggest feeding with the baby on a slant, so their head is above their belly.
However, it can be that they don’t like the flow level of the food. Are you breast feeding or bottle feeding? If bottle feeding, it might be the nipple flow. If breast feeding, overactive letdown often causes fussy eating. My little one, for his first couple of months, would fuss everytime I had letdown. Now that he’s a little older, he gets impatient and fusses between letdowns!