O erro de login é porque o domínio não existe de acordo com qualquer DNS. A maneira suportada é baixar os aplicativos do Office separadamente da loja de aplicativos. Depois de baixado, você deve entrar e ativar o Office. As instruções de instalação estão detalhadas abaixo:
Instalar e configurar o Office em um iPhone ou iPad com o Office 365
Install and sign in to any Word, Excel, PowerPoint, or OneNote app on an iPhone or iPad for the first time
Your device must be running iOS 8.0 or later. App availability also varies by country. Find out what's available in your country
Important
To use the extra features in the apps, you must sign in with the Microsoft account or work or school account that's associated with your qualifying Office 365 subscription. If you have an iPad Pro, you must also have a qualifying plan to do any type of editing on that particular device. See What you can do in the Office apps on an iOS or Android device with an Office 365 plan.
To learn more about Office apps on the iPad Pro, see the Office blog post Microsoft Office apps are ready for the iPad Pro.
If you haven't installed any of the Office apps on your iPhone or iPad as yet, download one, or all of them from the Apple App Store.
Word
Excel
PowerPoint
OneNote
Once you download it, tap any Office app to open it. Swipe through the introduction, and tap Sign In.
To use the extra features in the app, on the Sign in page, type the personal Microsoft account or work or school account associated with your Office 365 subscription, and then tap Next.