I just bought Microsoft Office365 Home account and found the error message like “No subscription found” when I try to activate it on my iPad. I have find out the solution from Mark on Apple communities.
The solution is easy, you may try. Just open Microsoft office app (eg. Word) on your iPad, click on “Connect” and connect it with your OneDrive account. It will show the username and password for you to enter your Microsoft account. And after connect with OneDrive, the program will activated itself.