Issue while inserting Data in Firestore using cloud workflows firestore connector with Json object coming from previous step which is a cloud function

I am trying to build a workflow where in step1 I am running a cloud function which returns a Json Object in the form of python dictionary and I want the same to be inserted in Firestore using firestore connector. But I am getting the below error:

    HTTP server responded with error code 400
    in step "create_document", routine "main", line: 27
    HTTP server responded with error code 400
    in step "create_document", routine "main", line: 28
    {
      "body": {
        "error": {
          "code": 400,
          "details": [
            {
              "@type": "type.googleapis.com/google.rpc.BadRequest",
              "fieldViolations": [
                {
                  "description": "Invalid JSON payload received. Unknown name \"field1\" at 'document.fields[0].value': Cannot find field.",
                  "field": "document.fields[0].value"
                },
                {
                  "description": "Invalid value at 'document.fields[1].value' (type.googleapis.com/google.firestore.v1.Value), 200",
                  "field": "document.fields[1].value"
                },
                {
                  "description": "Invalid JSON payload received. Unknown name \"Alt-Svc\" at 'document.fields[2].value': Cannot find field.",
                  "field": "document.fields[2].value"
                },
                {
                  "description": "Invalid JSON payload received. Unknown name \"Cache-Control\" at 'document.fields[2].value': Cannot find field.",
                  "field": "document.fields[2].value"
                },
                {
                  "description": "Invalid JSON payload received. Unknown name \"Content-Length\" at 'document.fields[2].value': Cannot find field.",
                  "field": "document.fields[2].value"
                },
                {
                  "description": "Invalid JSON payload received. Unknown name \"Content-Type\" at 'document.fields[2].value': Cannot find field.",
                  "field": "document.fields[2].value"
                },
                {
                  "description": "Invalid JSON payload received. Unknown name \"Date\" at 'document.fields[2].value': Cannot find field.",
                  "field": "document.fields[2].value"
                } 

This is how my workflow looks like

main:
    params: [args]
    steps:
        - step1:
            call: http.get
            args:
                url: https://XXXXXXXXXXXXX.cloudfunctions.net/step1-workflow
                query:
                    bucket_name: ${args.bucket_name}
                    blob_name: ${args.blob_name}
            result: key_val
        - step2:
            assign:
                - project_id: ${sys.get_env("GOOGLE_CLOUD_PROJECT_ID")}
                - collection: "a-dummy-collection"
                - document: "new7-dummy-document"
        - create_document:
            call: googleapis.firestore.v1.projects.databases.documents.createDocument
            args:
                collectionId: ${collection}
                parent: ${"projects/" + project_id + "/databases/(default)/documents"}
                query: 
                    documentId: ${document}
                body: 
                    fields: ${key_val}
            result: inserted

if in place of ${key_val} I use simple json {"field1": {"stringValue": "str1"},"field2": {"integerValue": 10}} it works fine and data gets inserted in the Firestore but if I try to use the object from variable ${key_val} which is in the same structure as mentioned json it gives error.

Answer given in the comments: the ${key_val} result from the call to the cloud function is actually returning the whole response object, not just the body. That's why in the error messages, you were seeing things like content-type and other headers.

The solution here is to say that we want the body of that response with: ${key_val.body}.