Unfortunately I think you're going to need to backtrack and take another approach. The neo4j-doc-manager was an open source project which is no longer maintained (GitHub - neo4j-contrib/neo4j_doc_manager: Doc manager for Neo4j) and probably this is failing because it is not using anything close to a recent software stack for Neo4j.
As a result, I'd consider either leaning on the APOC approach, or exporting MongoDB data to JSON and then using apoc.import.json