Before trying to migrate a database to Azure SQL Database please perform an assessment using Data Migration Assistant (free tool). Resolve all blocking points before proceeding to migrate to Azure SQL. The same tool can help you with the migration, especially with such a small database, but you can also use Data Migration Service, in case you would like to consider opting for an online migration.
I have received that error when Windows logins are referenced on the database or when your are using SQL Server Management Studio is used to migrate the database to Azure but you are using an old version of SSMS (if that is the case upgrade to the latest version).