Common fields list the fields that are common in both source and target. You can assign masking rules to all the common fields.

The missing mandatory fields list the target mandatory fields that are missing in the source. To mask the missing mandatory fields, you can configure an expression or specify a value in the expression builder.

For example, you need to populate the target with data for testing purposes. You create a mandatory field called AlternatePhone_c in the target Account object that is not present in the source. When you run a

masking

task, you need to populate the missing mandatory target field with a value. The task fails because the mandatory field is missing in the source. You can enter a specific value or configure an expression for the missing mandatory field to populate the target.