Parse Error: The server returned a malformed response – Error: Parse Error: Expected HTTP/ – when trying to access one of my app URLs with postman

I am managing an app built by third parts in python.

I have this url dispatcher

urls += [(r'/path/objectAlpha/(.*)', objectAlphaHandler)]  # this was made by third parts, it is expected to work

and this class

class objectAlphaHandler(BaseHandler):

    def __init__(self, application, request, **kwargs):
        super(objectAlphaHandler, self).__init__(application, request, **kwargs)  # do the init of the basehandler

    @gen.coroutine
    def post(self, action=''):
        response = {}
        
            ...     
            
            response = yield self.my_method(json_data)
        
            ... 

        self.write(json.dumps(response))

    def my_method(self, json_data)
        ...

I want to check that the app correctly receives the request and returns some response.

So I try to access that url with Postman

request type:

POST

URL:

http://<machine_ip>:<machine_port>/path/objectAlpha/

I get this error from Postman response box

Parse Error: The server returned a malformed response

and when I click on "view in console" I see

POST http://machine_ip>:<machine_port>/path/objectAlpha/
Error: Parse Error: Expected HTTP/
Request Headers
Content-Type: application/json
User-Agent: PostmanRuntime/7.28.4
Accept: */*
Postman-Token: d644d7dd-699b-4d77-b32f-46a575ae31fc
Host: xx.xxx.x.xx:22
Accept-Encoding: gzip, deflate, br
Connection: keep-alive
Request Body

What does Error: Parse Error: Expected HTTP/ mean?

I checked my app logs but it seems it is not handling any request, even if Postman indicates that the server is returning a (malformed) response.

I also tryed to chenge the target url to:

https...

but it returns

 Error: write EPROTO 28427890592840:error:100000f7:SSL routines:OPENSSL_internal:WRONG_VERSION_NUMBER:../../third_party/boringssl/src/ssl/tls_record.cc:242:

which I found out it indicates I should stick with HTTP

Then I tried also:

http://<machine_ip>/path/objectAlpha/

and

<machine_ip>/path/objectAlpha/

which generically return:

Error: connect ECONNREFUSED <machine_ip>:80

I also tryed to substitute line

urls += [(r'/path/objectAlpha/(.*)', objectAlphaHandler)]  

with

urls += [(r'/path/objectAlpha/', objectAlphaHandler)]  

and

urls += [(r'/path/objectAlpha', objectAlphaHandler)]  

but none of these worked.

What is wrong? How can I fix it?

UPDATE

Apparently, according to this thread on Postman Github, the problem happens only on Postman Desktop and not on Postman on browser.

So I tryed to send the request form Postman on my browser but I get

 Cloud Agent Error: Can not send requests to reserved address. Make sure address is publicly accessible or select a different agent.

because, according to this other thread,

Postman Website cannot send a request to your computer’s localhost. It first needs to connect to your PC with the Postman desktop client

and even if I follow the indications in that answer

Run it [ndr. Postman desktop], then go to the Postman workspace in your browser -> send the request and it will work.

I still get the same

Error: Parse Error: Expected HTTP/

on both Postman Desktop and Postman on browser.

UPDATE

Going on debugging, I tryed to cast a curl on that URL from my terminal:

myuser@mymachine-VirtualBox:~$ curl --verbose "http://<target_machine_ip>:<target_machine_port>/path/objectAlpha"

and I got:

*   Trying <target_machine_ip>:<target_machine_port>...
* Connected to <target_machine_ip> (<target_machine_ip>) port <target_machine_port> (#0)
> GET /orkpos5/receipt HTTP/1.1
> Host: <target_machine_ip>:<target_machine_port>    
> User-Agent: curl/7.74.0    
> Accept: */*    
>     
* Received HTTP/0.9 when not allowed  
    
* Closing connection 0    
curl: (1) Received HTTP/0.9 when not allowed