Sharing Outlook calendar with a business O365 account

Hi All,

I have a customer who just received a calendar share invite from an Outlook account. The user currently has a O365 business account. When she tries the link to add the calendar it prompts her to enter in credentials for a Microsoft account. She enters in her O365 details but Microsoft returns a error stating it does not recognize the account. 

Can O365 users view and edit calendars from Outlook accounts? If so are there any settings or configuration that needs to be changed in the O365 admin console for this to work.

Thanks in advance!