"An argument was invalid"

Hello !
I was upgrading my supporter pack little by little but when i'm trying to upgrade into "Thaumaturge of the vaal" or "Warlord of the Karui" There is the message "An argument was invalid" next to shipping fee and i can't continue the transaction.
I saw that others people have this problem but was wondering if there is a fix to this.
Have a nice day/evening !