Breast milk fed baby “refusing” formula?!

So, I have been exclusively pumping and feeding, but here recently, my supply has dropped & im not making enough for the baby. I’ve decided to supplement with formula through the night so I’m not pumping and feeding and having to sit up another 30 mins while the baby’s food settles (she has reflux). But, tonight was the first night I decided to start supplementing, well, I’m only on the 1st feeding of the night, & my baby wasn’t happy at all while getting formula! Is this a thing? She kept coughing & letting the formula run out of her mouth as well as spitting it back out! I got most of it down, but she just didn’t seem as happy as she does with breast milk. I didn’t think this was going to be a problem, as I had been adding half a scoop to my breast milk for the extra calories (I don’t produce a lot of fatty milk). But now I feel bad for giving her formula. She has a lip tie, & I will be seeing an ENT to get it fixed in hopes she can actually start nursing without it being super painful. But, does anyone know why this may be?! I don’t want to give her formula if she hates it!