I have created new document channel after running after extraction error at reconcile process model in node set var.
Discussion posts and replies are publicly visible
Based on the error details looks like for the document you sent for extraction does not have a structure (CDT) defined in Appian or it is not configured correctly. pv!documentCDT.value --> will hold the structure of the CDT for the document that was classified and sent for extraction. Since this field does not have any value (related CDT structure is missing) the function fails.
After adding new channel, did you complete all the steps required for adding a new document type to it as documented below -
https://docs.appian.com/suite/help/21.4/idp-1/adding-a-new-document-type.html