the plug is actually not so easy to mount. luckily, I tried before removing the blue plastic liners. I ended up plugging the battery in before glueing it in place, just to be sure I could connect it at all, which worked fine for me.
also, I recommend checking if the battery loads and whether the phone still works, before glueing the back cover on the phone
haha, the same happened for me after using a hair dryer. While still hot, the paint peeled of very easily. (too bad the mid-frame visually blocks most of the circuits…)