REST connector POST

I'm trying to configure the REST connector to make a POST call, but I can't quite figure it out.
The URL is http://xx.xx.xx.xx/girh_api/gt/post/id/modifica_tancament/tancament_id/3. I put this in the POST URL section.
As a parameter (in postman it would be the body section), there is a parameter (the change I want to make): state = "New state".
I understand that to add parameters it is done in the "Payload" section and with "content type".
I have tried different Content Type and Payload but it just doesn't work for me.
As a last requirement, in postman I add a header, which I understand goes in the headers section of the connector.
I have tried making the call with Postman and it works, but I can't do it with the Bonita connector.
The result is:
http://xx.xx.xx.xx/girh_api/gt/post/id/modifica_tancament/tancament_id/3 response status is not successful: 400 - Bad Request.
Any help/examples would be welcome. Thank you so much.