Bought PSE 13 for mac on Amazon... can't install?

I have downloaded my newly purchased copy of Photoshop Elements 13 for Mac from Amazon.... I have it but can't figure out how to install it. Help!

I have an installer (I think that is what it is) labeled "PhotoshopElements13.dmg"

When I get to the serial number screen I cannot get any further as I don't have one...

I have a product key... but that does not work.

HELP!