Share file to external contact

I am trying to setup my O365 tenant to enable users to easily share files with our sister company. I have imported all of their users as Office 365 Contacts and they appear fine in Outlook, however in OneDrive they do not appear when I try to share a file with them. External sharing is enabled and it works if I enter their full email address.

Does anyone know if it is possible for OneDrive to look up contacts when sharing a file?

Oscar has been created as a contact in Office 365 Admin Centre

I have created an Office 365 Contact for Oscar.

If I search for Oscar he does not appear when sharing a file in OneDrive

But when I search for Oscar when sharing a file in OneDrive he does not appear.