After restoring the SQL Server Database from one server to another server, SQL Server Login id and Database user id does match, so it look like a orphaned user, to fix the issue then follow the commands
-Script to view difference in SID
USE MASTER
GO
SELECT name as SQLServerLogIn,SID as SQLServerLogInSID FROM sys.syslogins
WHERE [name] = 'TestUser3'
GO
USE AdventureWorks
GO
SELECT name DataBaseUserID,SID as DatabaseUserSID FROM sysusers
WHERE [name] = 'TestUser3'
GO
--Command to generate list of orphaned users
USE adventureWorks
GO
sp_change_users_login @Action='Report'
GO
--Command to map an orphaned user
USE AdventureWorks
GO
sp_change_users_login @Action='update_one',
@UserNamePattern='TestUser1',
@LoginName='TestUser1'
GO
