To use the Passthrough feature your component descriptor must be modified and rebuild using the sailor version 2.1.0 or above.
What is Passthrough?
With an introduction of Passthrough feature, it is now possible to use and map the fields using data from the previous step(s).
To benefit from the Passthrough feature there must be at least 3 components in the integration flow.
More details about passthrough are provided in the series of guides.