Introducing Formula Milk

Just wanted to ask how did you successfully introduce formula milk to your baby? My lo is turning 8 months, breastfed, and I tried giving him Nan Optipro HW but he refuses the bottle. He’s tried drinking my breast milk through bottle as well, and there’s been no problem. Please help! I want to slowly transition him to formula in case I needed to go somewhere and I have no stash left. Thank you! #advicepls #theasianparentph