@sakuraime Welcome to Microsoft Q&A and Thank you for posting your question.
If you are trying to migrate from SQL server to SQL Managed Instance, please go through Migrate SQL Server to SQL Managed Instance offline with PowerShell & Azure Database Migration Service and verify you did not miss any steps. There are a few additional requirements you need to address:
Select logins. Create a list of logins to be migrated as shown in the following example:
$selectedLogins = @("user1", "user2")
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