My app has been free since the beginning, I uploaded a new version and set it to Teir 1 pricing.
People who updated got it for free for some reason, only new downloads by new users were charged.
Did I miss something in my main bundle to ensure that upgrades are not free?
It seems you cannot charge users for updates, so if they have downloaded your app once for free they will be able to update it also.
I think the only option to introduce payments in free apps is to include in-app purchase in them.