An Azure relational database service.
Please make sure you are "restoring" (importing) the database with a different name as the source database from where the bacpac was created. Importing database cannot replace existing databases.
In addition, as a workaround, Try using PowerShell instead of the portal.
New-AzureRmSqlDatabaseImport –ResourceGroupName “sqlgroup” –ServerName “powershellserver” –DatabaseName “mypowershelldatabase” –StorageKeytype “StorageAccessKey” –StorageKey $primarykey -StorageUri $StorageUri –AdministratorLogin $credential.UserName –AdministratorLoginPassword $credential.Password –Edition Basic –ServiceObjectiveName B -DatabaseMaxSizeBytes 50000
Finally, make sure the access tier of the bacpac on Azure Storage is type "Cool".