Response does not include refresh token

Response does not include refresh token

I have created a "server-based application".
I ran the code on terminals.

`` `
$ curl -X POST https://accounts.zoho.com/oauth/v2/token \
-F "grant_type = authentication_code" \
-F "client_id = {client_id}" \
-F "client_secret = {client_secret}" \
-F "redirect_uri = {redirect_uri}" \
-F "code = {code}"
`` `

The response does not include the update token.
`` `
{
 "access_token"： "1000.XXX.XXX"、
 "api_domain"： "https://www.zohoapis.com"、
 "token_type"： "Bearer"、
 "expires_in"：3600
}
`` `

"Self-client" will return a refresh token.
I do not know why. can you tell me?