Add-DatabaseToAvailabilityGroup : Exclusive access could not be obtained because the database is in use. RESTORE DATABASE is terminating abnormally.

Environment: SharePoint 2016 OnPremise Farm

Issue: Error when adding content database to SQL Always on Availability group using the following PowerShell command

Add-DatabaseToAvailabilityGroup -AGName AGSP1 -DatabaseName SPContentDB -FileShare \\UTI01\AlwaysOnShare

Error: Add-DatabaseToAvailabilityGroup : Exclusive access could not be obtained because the database is in use.
RESTORE DATABASE is terminating abnormally.


Fix: Make sure the content database in the secondary database has been removed before executing the above PowerShell command.