When trying to install AOE3 with play on linux, it goes well until the moment I have to enter the CD key. Here, it says I should enter a 25 characters long key (which I have) in five boxes of - logically - 5 characters each. But the first and last ones only accept 4, and I get stuck with my remaining 2 extra charatcers. Of course, in this situation, the key is not recognised.
That is one of the strangest things I've heard of. Do you have a screenshot?
So is there an error when you enter the 5th character?
Is the Key screen cut off by the virtual desktop or the screen?
Have you tried copy & paste?