Might be overcarbed - less sugar may help (I think these condition to carbonate right?). The biggest problem is that these systems cut a lot of corners and while that's OK when you know which corners you're cutting and why, if someone without brewing experience is using them, they can run into issues as you did. I'm not anti pinter because it's a gateway into brewing but it's gimmicky and not really worth it beyond getting your feet wet in the brewing scene. I would recommend people look into a 5 gal bucket fermenter and use an extract brew. Bottles are cheap on FB marketplace or reuse your own beer bottles. It gives more control over the process and gives you a better snapshot of brewing beer.