Http POST node error: 422 - Failed to deserialize the JSON body into the target type: missing field

Questions
1

Describe the problem/error/question

I am trying to hand over a vector to a POST http request node.
The vector is actually coming from an ebbeding model that I run to turn my query into a vector to then retrieve the answer from my chromadb.
But I simplified it here replicating the same error with a much simpler setup.
I always get the error immediately after executing the http request.
In the end I made a very simple simulation with only two nodes: a Set or Code node and the POST node. This would replicate the error.

My input data looks like this:
[{
“query_embeddings”: [[ 1,2,3,4 ]],
“n_results”: 5,
“include”: [
“metadatas”,
“documents”
]
}]

I tried a lot to change specific format bits as gemini and chatgpt told me to:
making distinctions between array and top-level object and that subtle difference — [] wrapping the object — causes the 422. Nothing helped.

In the expression editor eveything looks good:
expression
{{ $json }}
result
[Object: {“query_embeddings”: [[1,2,3,4]], “n_results”: 5, “include”: [“metadatas”, “documents”]}]

The error message: 422

"{
    "error":"ChromaError",
    "message":"Failed to deserialize the JSON body into the target type: missing field `query_embeddings` at line 1 column 7"
}"

Request:

{ "body": { "": "" }, 
  "headers": { 
    "accept": "application/json,text/html,application/xhtml+xml,application/xml,text/*;q=0.9, image/*;q=0.8, */*;q=0.7" 
  }, 
  "method": "POST", 
  "uri": "http://192.168.10.123:8060/api/v2/tenants/default_tenant/databases/default_database/collections/<mycollectionid>/query", 
  "gzip": true, 
  "rejectUnauthorized": true, 
  "followRedirect": true, "resolveWithFullResponse": true, 
  "followAllRedirects": true, 
  "timeout": 300000, 
  "encoding": null, 
  "json": false, 
  "useStream": true
}

My two nodes

n8n setup

  • n8n version: 1.101.2
  • Database (default: SQLite):
  • n8n EXECUTIONS_PROCESS setting (default: own, main):
  • Running n8n via (Docker, npm, n8n cloud, desktop app): Self hosted npm
  • Operating system: Debian Bookworm
2

I don’t know what you are working with, but I think you missed some parameters in your query_embeddings fields. You can check the documentation if you have it

3

‘Working with’ ? Where ? What do you mean. The database? I filled the database myself. It’s a RAG system.
The error says

missing field `query_embeddings`

But there clearly is a field query_embeddings which contains a vector. So the database isn’t questioned at all.