Inability to use mints to upgrade power mints

I believe there is a bug or a problem in using the mints as a way to upgrade the power mints, as it is said when I got a mint in the tournament— mints is used to buy and upgrade power mints but upon unlocking all the power mints in pvz 2 I saw that I am unable to use the mints for the purpose of upgrading my power mints, I am asking for the developers of EA games to have this fixed or if I can get an explanation on why this happens or if this is completely normal, I believe in my stance as I think that what is written in the game should be reliable, not misleading, and accessible in a way that we get the sense of freedom that this game provides. I am asking for help EA developers🙌🏻