Answered question

The first to do is to manually create your target server in NeoLoad. In the server list right mouse click and create a new HTTP server. Fill all the information regarding host and port and check SSL box if needed.

Then you just need to manually create a request in NeoLoad by right mouse click inside the Actions container or better inside a transaction that you have already created.

Change the request method from GET to POST. Change the "Post content type" from "Form" to "Text".

Copy/Paste your JSON data inside the "Text content" field.

Click on the Advanced button of the request and go to the Headers tab. Add a new line and use as name "Content-Type" and value "application/json"

You said that you need to pass authentication. Your credential can be added in the server definition that you have just created. If it's BASIC authentication you can fill the realm, username and password.

Another way is to manually add the BASIC authentication header in your request with your username:password hashed using Base64.

The syntax is:

Authorization: Basic <BASE64 hash>