I can't refresh token

I can't refresh token

I am using postman to test apis that I will be putting into  an applciaton and I am having issues getting my refresh request to work -the redirect_uri is https://www.getpostman.com/oauth2/callback (is this correct? what should it be) and what should Authorization be set to? I currently have it set to Bearer access_token

https://accounts.zoho.com/oauth/v2/token?refresh_token={{Zoho_RefreshToken}}&
client_id={{client_id}}&
client_secret={{client_secret}}&
scope=Desk.tickets.ALL, Desk.settings.READ, Desk.basic.READ&
redirect_uri={{redirect_uri}}&
grant_type=refresh_token