Baby drinks, swallows and breathes using their natural rhythm, like at the breast. Natural Response Nipples are different from free-flow nipples and like breastfeeding, it could take a few tries to get it right. That's perfectly natural.
If you have tried the same nipple a few times with little or no success, it may mean your baby needs a different nipple flow. The flow of milk is linked to how enthusiastically or steadily they drink as they develop, regardless of age.
Does your baby seem frustrated or fall asleep during feeds? Try a higher flow rate. Is your baby gulping or milk leaking from their mouth? A lower flow rate may help.