My customer has a copy of Office Home and Student 2013 on a PC. She has recently purchased a Mac Powerbook, and a copy of Office Home and Business 2016, Mac edition (product keycard). When she attempts to install the new software on her Mac - following the instructions on the keycard - it prompts her for her MS account. On entering this, a page appears showing her as having bought Office 2013 Home and Student. It asks her for the Office product key; on entering the PK for Office 2016/Mac and selecting Install, she then gets a message telling her that it can't be installed, because it's for an unsupported OS.

Can anyone advise a procedure which will allow the installation?