$vectorSearch is not allowed

MongoDB Atlas Vector Search
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2

I have the same problem however my code worked a few weeks ago. I also use MongoDBAtlasVectorSearch from LangChain. I did some research and found out that even direct querying from Atlas UI page using $vectorSearch doesn’t work anymore.

My search index looks like this

{
    "mappings": {
        "dynamic": false,
        "fields": {
            "embedding": {
                "dimensions": 1536,
                "similarity": "cosine",
                "type": "knnVector"
            },
            "location": {
                "type": "geo"
            }
        }
    }
}

There is also a geo-index part here but it doesn’t matter. Here is the search query:

{
    "$vectorSearch": {
      "index": "vector_geo_index",
      "path": "embedding",
      "numCandidates": 10,
      "limit": 2,
      "queryVector": [...]
    }
}

Error: Failed to run this query. Reason: $vectorSearch is not allowed or the syntax is incorrect, see the Atlas documentation for more information

This did work previously. Also, the old (deprecated in favor of $vectorSearch) knnBeta operator works fine:

{
    "$search": {
      "index": "vector_geo_index",
      "knnBeta": {
        "vector": [...],
        "path": "embedding",
        "k": 2
      }
    }
}

My guess it is not related to Langchain. It is probably something on the Atlas side. Docs say that the vector search is a preview feature and not recommended for prod. Maybe it is not very stable at the moment.