The /refresh endpoint is used to refresh a valid token. The response from this endpoint is identical to the login endpoint and will return your user token, a refresh token and an expiry time. The expiry time will be the amount of time the assigned token will live. You can use the the refresh toke on this endpoint to retrieve a new token without having to login.
Below is an example response from the Refresh endpoint
"expiresAt": "new_sample time",
The expiresAt time seen in the response above indicates when the userToken included will be invalidated this happens 15 mins after token creation. Hitting the refresh endpoint within the 15 min expiration will issue new tokens.