My tub has peeling patches all over,
You have to remove all the old paint first. My sister has done hers twice now and still keep peeling over time. Not to sure if it is worth doing it yourself.
Have to remove old and CAREFULLY follow directions on new resurfacing can. Either that or call in a company that does it for you with a warranty.
All painted tubs will eventually peel, even the ones prof done. That's why they only give a 1 year warranty. Time to replace or strip it and leave it unpainted.
This article may help https://homeguides.sfgate.com/repair-peeling-finish-bathtub-25256.html
You'll have to remove the peeling stuff as much as possible. Sand the edges and then use a tub painting kit from a home improvement store. Or better yet, have a pro do it which will last longer.