How to move user from a CSP Exchange Online licence to a Microsoft direct licence in the same tenant

Both subscriptions provide the same Exchange Online Plan 1 product in one tenant, so Microsoft 365 combines the available seats. A user is assigned the product SKU, not a reseller or billing subscription; there is no supported control that pins this mailbox to the Microsoft-direct seat. Because the direct subscription is active and two equivalent seats now exist, do not remove and reassign the user. Microsoft’s transition guidance says equivalent offers with the same license count in the same tenant need no reassignment and should not interrupt service or data. Coordinate cancellation or non-renewal of the CSP subscription, then verify the direct subscription remains Active, at least one Exchange Online Plan 1 seat remains, and the user still shows the license. Do not delete the user or mailbox. If the closed CSP cannot cancel its subscription, open a Microsoft 365 billing request with both subscription IDs and the partner-closure notice.