Refresh token method in Sony's Lifelog API returning 500 error

Question

I'm trying to use the refresh_token for sony's lifelog api but it's returning 500 error. I'm sending the request to https://platform.lifelog.sonymobile.com/oauth/2/refresh_token

My request is:

POST /oauth/2/refresh_token HTTP/1.1
Host: platform.lifelog.sonymobile.com
Cache-Control: no-cache
Content-Type: application/x-www-form-urlencoded

refresh_token=[MY_REFRESH_TOKEN]&grant_type=refresh_token&client_id=[MY_CLIENT_ID]&client_secret=[MY_CLIENT_SECRET]

The response is:

{
"fault": {
    "faultstring": "Execution of ServiceCallout CheckRefreshTokenStatus failed. Reason: ResponseCode 500 is treated as error",
    "detail": {
        "errorcode": "steps.servicecallout.ExecutionFailed"
        }
    }
}

I have no issues with authenticating or using the API otherwise, it's just this call that's giving me errors.