Python Zeep wsdl call giving Unable to cast object of type 'System.Xml.XmlNode[]' to type 'System.IConvertible'

Question

I am getting error "Unable to cast object of type 'System.Xml.XmlNode[]' to type 'System.IConvertible'." with the below webservice call (python 3.6/Zeep Client). The issue is that req_opt_doc_item1 & req_opt_doc_item2 could not be evaluated with "Val". Without it the call is successful though I am not able to get the desired results. Both are integer types as per the wsdl. I am thinking it is not do with the data type but req_opt_doc_item1 & req_opt_doc_item2 could not be passed as array with two elements in them.

What am I missing here?

def load_documents(doc_id):
    try:

        cws_req_doc_info_id = {
            'CWS_REQ_DOC_INFO_ID': ['DocTitle', 'DocDelTstamp', 'DocContent'],
        }

        req_doc_info = {
            'DocId': doc_id,
            'ReqInfo': cws_req_doc_info_id,
        }

        req_opt_doc_item1 = {
            'Id': 'OutputFormat',
            'Val': 3,
        }

        req_opt_doc_item2 = {
            'Id': 'LoadDDocType',
            'Val': 0,
        }

        cws_req_opt_doc_item = {
            'CwsReqOptDocItem': [req_opt_doc_item1, req_opt_doc_item2]
        }

        # Prepare the ReqOptDoc data
        req_opt_doc = {
            'Options': cws_req_opt_doc_item
        }

        # Construct the request payload
        load_doc_contents = {
            'UserCredential': user_credential,
            'ReqDocInfo': req_doc_info,
            'ReqOptDoc': req_opt_doc
        }

        # print(load_doc_contents)

        response = client.service.LoadDocContents(**load_doc_contents)
        return response

    except Exception as wsdl_err:
        cyp.write_log_file(True, True, email_id, this_script_name, str(wsdl_err) + '\n')
        exit(-1)

Called with below

    {
       "UserCredential":{
          "CredentialType":"UserIdPassword",
          "DomainName":"XXXXXXX",
          "UserName":"XXXXX",
          "Password":"XXXXX",
          "CypWsUserId":"",
          "CredentialData":""
       },
       "ReqDocInfo":{
          "DocId":"13930063  ",
          "ReqInfo":{
             "CWS_REQ_DOC_INFO_ID":[
                "DocTitle",
                "DocDelTstamp",
                "DocContent"
             ]
          }
       },
       "ReqOptDoc":{
          "Options":{
             "CwsReqOptDocItem":[
                {
                   "Id":"OutputFormat",
                   "Val":3
                },
                {
                   "Id":"LoadDDocType",
                   "Val":0
                }
             ]
          }
       }
    }

Tried to initiate a Webservice call to get the response from the server. The request message is having a cast issue.