Some Microsoft 365 subscriptions contain service plans that are not allowed to be assigned to a user at the same time. When this happens, a Microsoft 365 service plan conflicts with another Microsoft 365 service plan.
Assignment errors can only be resolved by Microsoft 365 administrators; Microsoft 365 does not automatically resolve licensing conflicts.
The “Conflicting service plans” error occurs with group-based licensing. If license assignment is performed through PowerShell, the MutuallyExclusiveViolation error message appears.
Microsoft’s web page Product Names and Service Plan Identifiers for Licensing provides further guidance on this issue.