Legal right to "transfer" Office Professional Plus 2016 ?

I bought Office Professional Plus 2016 and I have the activation key. It was bought on Ebay and my key is in an Email I received from the seller.

I want to change my computer. The old computer will be donated to a person who doesn't need Office. Of course I would uninstall Office before donating it.

Do I have the legal right to install Office Professional Plus 2016 on a newly acquired computer? By the way, there is advice on the internet to login to my Microsoft Account (a personal account) to see if there is a license there. I cannot find the license in the Microsoft Account. Advice on the internet about navigating the account to find the license seems to be a bit obsolete but I imagine it should have been easy to find if it is in fact in the account.

Related question: If I am allowed to install it, where would I download the file? Most advice about downloading probably assumes the Microsoft Account has the license. Please help.

Update ... There are updates in my next message, below.

An update ... I used setup.office.com to install Office. After installing and attempting activation the message was that my activation key is not valid. If I uninstall on the old computer, which I have been hesitating to do, how long would I have to wait before the I can activate the same key on this new computer, or will the answer be that I will never be allowed to activate on the new computer?

An update ... I uninstalled Office on the old computer. A few minutes later I tried internet activation again on the new computer. It failed. I will try phone-based activation now. Phone-based activation is now on the internet. It doesn't work either.

Depends, was the purchase of the key a very low cost key? If so, it's probably a MAK key that hit it's limit and won't activate. If it were a retail key, you should be able to move it from one computer to another. But that would have been in the ballpark of $400+ for Office 2016 Professionally Plus.

have you checked in your outlook account and removed the old system from your account
then check within your outlook account for installed software and see if Office 2016 is there

you can then remove/detach office 2016 from your account then install and activate office 2016 on your new system.

best of luck Steve ..