"message": "JSON request body must be an object at [line:1, column:2]","errorCode": "JSON_PARSER_ERROR"

Question

I attempted to send an HTTP request and transmit a JSON to the Salesforce REST API in the following manner, but encountered the following error:

Error: [ { "message": "JSON request body must be an object at [line:1, column:2]", "errorCode": "JSON_PARSER_ERROR" } ]

I have confirmed that the message is sent in JSON format. How can I correct this error?

This is my Apex code：

@RestResource(urlMapping='/apex_rest_api_endpoint/*')
global with sharing class CreateTask {

    @HttpPost
    global static String receiveAndProcessData(String jsonBodyList) {

        Map<String, Object> requestData = (Map<String, Object>) JSON.deserializeUntyped(jsonBodyList);
        
        String lineUserId = (String) requestData.get('userId');
        String lineChannelId = (String) requestData.get('channel');

And my python code：

def get_json_msg(event, context):

    if validate_signature_taichung(event['headers']['x-line-signature'],event)==True:
                    
            data = {
                'userId': get_line_userid(event, context),
                'message': get_line_message(event, context),
                'channel': "xxxxxxx"
            }


    elif validate_signature_taipe(event['headers']['x-line-signature'],event)==True:

            data = {
                'userId': get_line_userid(event, context),
                'message': get_line_message(event, context),
                'channel': "xxxxxxx"
            }

    json_body = {"jsonBodyList": data}

    return json.dumps(json_body)

def send_msg_to_customapi(event, context):

    json_msg = get_json_msg(event, context)

    print(json_msg)

    params = {
        "grant_type": "password",
        "client_id": "xxxxxxxx", # Consumer Key
        "client_secret": "xxxxxxxx", # Consumer Secret
        "username": "xxxx@xxxxx", # The email you use to login
        "password": "xxxxxxxx" # Concat your password and your security token
    }
    r = requests.post("https://login.salesforce.com/services/oauth2/token", params=params)
    
    access_token = r.json().get("access_token")
    instance_url = r.json().get("instance_url")

    headers = {
        "Authorization": f"Bearer {access_token}",
        "Content-Type": "application/json"
    }

    # Salesforce Apex REST API URL
    api_endpoint = f"{instance_url}/services/apexrest/apex_rest_api_endpoint"

    # HTTP POST
    response = requests.post(api_endpoint, headers=headers, json=json_msg)

Answer 1

When using method parameters in Apex, the parser expects a top level object that has a request element. In other words:

json_body = { 'request': { 'jsonBodyList': data } }

Further, you're double encoding the JSON, which is why you got a String data type. Do not use json.dumps:

return json_body