Can you share the error that you are receiving? A screen shot of the message at the device would be fine.
Also, can you confirm if you are using a Custom Domain Account for Office365? I suspect that the structure of the log in/account type may be where the trouble lies.
The app. uses login credentials associated with Office365 accounts purchased directly through MS or custom domain accounts. If they are using a custom domain account, please see the article posted here: http://www.support.xerox.com/support/APP_STUDIO/support/en_US.html?objGUID=3082 (Note: Office 365 will not work if the customer is using Active Directory Federated Services. ADFS is not supported at this time.)
If you are using the standard credentials provided by onmicrosoft.com, the login process is straight forward.
If you are using a Custom Domain account, it's a little trickier. For the domain portion, you need to do a little hunting as to how the account is setup. The domain is typically the first part of the SharePoint online URL that you use (something like: https://mydomain.sharepoint.com).
For example, if the account was created with mydomain.com and users are in that domain, the login will be very easy and the domain will not need to be added to the login screen. just login with email@example.com and it should work fine.
If another domain was added to mydomain.com or the domain was changed, this is where the complexity comes in. For example, if they have added a domain called theirdomain.com the user will login with mydomain\firstname.lastname@example.org. If you'd like to share your UserID, I might be able to help with the structure of your login.