i have Exchange server 2019 hybrid mode with microsoft 365 online which is working fine like email sending and receiving from both end.

i have 1100 users on Exchange online 365 and wanted to move 400 mailboxes from microsoft online 365 to Exchange On-Prem 2019 CU14.

when i m trying to move getting error “TargetUserAlreadyHasPrimaryMailboxException: Target user ‘6f5ab530-2740-488c-b165-5cebb5a05’ already has a primary mailbox.”

can anybody advise its reason as i am doing R&D from few days read so many articles over google but not getting out of this.

tried some changes but not success i want to resolve this