Hi @Olaniyi FAGBOLADE ,
Linking Microsoft accounts is no longer supported:
https://support.microsoft.com/en-us/help/4028404/microsoft-account-linking-accounts
What you can do instead is create an alias and logon with that:
https://support.microsoft.com/en-us/office/add-or-remove-an-email-alias-in-outlook-com-459b1989-356d-40fa-a689-8f285b13f1f2
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Best regards,
Leon