Azure AI Document Intelligence - Studio finds key-value pairs, but code has keyValuePairs as None - how do I enable this?

I have a bunch of files with the same format from which I'm trying to extract key:value pairs in batch. It appears that in the document intelligence studio I have to do this for every document separately, which is not feasible given the number of documents, so I've switched to using the python API. I'm trying to activate the keyValuePairs feature but despite my best efforts it isn't working. I found something that said it doesn't work with markdown output, which is why I'm specifying text here.

formPath = "path to my file"
with open(formPath, "rb") as f:
        base64_encoded_pdf = base64.b64encode(f.read()).decode("utf-8")
        
document_intelligence_client  = DocumentIntelligenceClient(
    endpoint=endpoint, credential=AzureKeyCredential(key),
    features = ['keyValuePairs'], #is this how to specify this? Can't find in documentation so this is copied from online somewhere.
    output_content_format=ContentFormat.TEXT
)
poller = document_intelligence_client.begin_analyze_document(
    "prebuilt-layout", AnalyzeDocumentRequest(bytes_source = base64_encoded_pdf)
)
result = poller.result()