Place the button inside of a dataview or listiview pointed to the ProductType entity. Then the button will get the ProductType parameter
I doubt about that like as you.
In case of object, most likely entity, it is much clear.
But for other types(eg. String, boolean and so one), I have no idea how to assign the parameter value that is defined in a microflow.
1.in case of creating an object
U can not get para from button . Usually u can new an object in a mircoflow and pass it to a page.
2.in case of editing an object
U can put edit button inside of a dataview and get the object.