SFTP Smart Service Plug-in External System Key

in the 3rd Party Credential (from Admin Console) you must define valid credential to reach out the SFTP location. According to the name you provide to the credential, Appian will give you the System key. That string is what you have to provide here

Here is the documentation link for the same

https://docs.appian.com/suite/help/19.2/Appian_Administration_Console.html#third-party-credentials

Thanks :)

Thanks :)