It could be 2 reasons: the milk or the baby. Try at which temperature your baby would like to have his milk. Also, check whether the teat is draining properly or you may want to change to a wider hole teat. Has your baby been unwell lately? Or maybe he is too distracted to drink from the bottle.
If he refuses he drink from the bottle, don't force him. You may try again later. They will drink when they are hungry but try to check first why he has refused the bottle in the first place. Hope this helps.
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