My issue - and one that appears widely acknowledged - is that none of my 365 accounts are accepted as Microsoft accounts and therefore cannot access the MS Store to purchase the upgrade. Try as I might, I cannot find an alternate method to purchase this upgrade and I do not fancy purchasing an upgrade through some obscure personal MS account.
So is it possible to complete purchases on the MS Store using either the 365 Admin account or a delegated user account on 365? Otherwise, is anyone aware of a method to purchase the W10 upgrade using at least an email address of one of my 365 accounts?