Cannot retrieve LWA code with sellerId and mwsAuthToken for SP-API, access denied


#1

I want to migrate our current application to hybrid application.
I try to use seller id and mwsAuthToken to get the LWA code in order to exchange for the LWA refresh_token where I found on the amazon migration guide. LINK

This is my request

https://sellingpartnerapi-fe.amazon.com/authorization/v1/authorizationCode?sellingPartnerId=[sellerId]&developerId=[developerId]&mwsAuthToken=[mwsAuthToken]

what I got from response is
{

    “errors”: [

        {

            “message”: “Access to requested resource is denied.”,

            “code”: “MissingAuthenticationToken”

        }

    ]

}

Not sure what I really missing? Can anyone help about this?