Registering Excel on iPad, when iTunes and Microsoft account emails differ? I have an Office 365 Home Premium subscription, and so I wish to use the subscription-based features of Excel for iPad.

The problem is that I use different email addresses for my iTunes and Office 365 subscriptions.

This is the series of steps I've followed:


Install Excel for iPad
Run Excel for iPad
Select "Buy Office 365 Home"
Select the tiny "I Already Have a Subscription"
Enter my iTunes Store password, for my iTunes email address


I then get the error message:


  "No Subscription
   This Apple ID doesn't have a paid Office 365 subscription."


For my two different email addresses, the domain names are the same, but the account names are specific to the two products - as an anti-spam measure, and to make it easier to detect phishing messages.

I considered changing my Apple email address to be my Microsoft one, or my Microsoft email address to be my Apple one. But in both cases, I would have a large number of login details to change, on multiple programs on multiple devices.

Are there any other alternative solutions, such as adding a second email address to either my iTunes or Microsoft accounts?
After days of looking, I've found the answer, via 
Having Problems Activating Office for iPad? Here’s a Simple Solution

Briefly:


Instead of saying “I already have a subscription”, choose the Read-only option
Then click on the Activate button at lower-left
Then you have an option to activate by using your Microsoft Office 365 account credentials


For me, doing this in Excel also activated my Word and PowerPoint iOS apps.