Ingest pipeline (attachment) unable to find base64 encoded field

Elastic Stack Elasticsearch
1

Hi!

I have a very basic ingest pipeline case where I'd like to call an attachment processor. A simple curl -X PUT with provided Json-data works perfectly but when I do the following from my c# code:

var response = await _docDb.IndexAsync<Document>(doc, i => i.Index("document").Pipeline("attachment").Id(doc.Id));

I get a:

field [ContentBase64Encoded] not present as part of path [ContentBase64Encoded]

The POCO is super simple with three public string properties:

public string? Id

public string? FileName

public string? ContentBase64Encoded

It seems like the attachment processor is unable to find my POCO property using the "field": "ContentBase64Encoded" specification.

What am I doing wrong here. I'm running v8.16 of Elasticsearch and the latest .Net sdk.

Many thanks!