Consider the following Microsoft Office for iPad scenario:
When you install Excel for iPad, Word for iPad, or PowerPoint for iPad, and then you start the app for the first time, it will sign you in automatically if you have used another Office for iPad app such as OneNote. The saved credentials from another Office for iPad app are used to sign you in automatically in order to minimize the barriers to get started. Therefore, you are not prompted for your user name and password.
The next dialog box that you see (if you do not have a subscription) asks you to "View for Free" or to buy a Microsoft Office 365 Home subscription.
View for Free
If you already have an Office 365 Subscription registered to a different email address, select View for Free, then select Activate to sign in again with the email address that has the subscription.
Buy Office 365 Home
If you select to buy a Microsoft Office 365 Home subscription, the next Buy Subscription dialog box has a Restore Previous Purchase option. When you click Restore Previous Purchase, you are prompted to enter your Apple ID, your password, or both.
Note: If your subscription purchase with Apple fails to complete, it is possible you have an unused purchase receipt from the Apple App Store. The restore process uses the unused purchase receipt (if there is one) to activate Office for your Microsoft account. The restore process is only applicable to restoring a purchase that you made from the App Store. As soon as Apple confirms your Apple account, you may receive the following message if you have not previously bought a subscription from Apple by using your Apple ID:
This Apple ID doesn’t have a paid Office 365 subscription.
This issue occurs because OneNote for iPad was previously installed on the iPad, and it had been signed into by using a Microsoft account. As a result, when Office for iPad is installed, the app uses the OneNote cached credential of the Microsoft account to sign in, and therefore you are unable to use your Office 365 Organization ID account.
To resolve this issue, following these steps:
Close all the Office for iPad apps. To do this, press the Home button on your iPad twice, swipe to find each Office for iPad app, and then swipe the preview screen up to close each app.
Go to iPad Settings.
In Settings, tap to select one of your Office for iPad apps such as Word, Excel, or PowerPoint.
Under RESET, tap Reset <app name>.
Slide to enable Delete Login Credentials.
Start one of your Office for iPad apps so that your credential is deleted.
Sign in using your Office 365 Organization ID account.
Note: You may need to delete the credential for each Office for iPad app.
Microsoft is researching this problem and will post more information in this article when the information becomes available.