This has been asked already and remains to be an issue

see: 

https://social.technet.microsoft.com/Forums/itmanagement/en-US/b7e445ec-78a0-4ffc-89e7-0a29b0691f87/product-key-needed-to-activate?forum=officeitpro

I'm unable to activate a trial of the subject version of office. I've tried everything referenced in the above link in both IE and Chrome. 

Please advise.

Hi,

This issue sometimes can be temporary, you can try it later to check the result.

You can also perform the steps on another computer, in another network environment, check if you can finally get the key displayed.

Regards,

Melon Chen
TechNet Community Su