https://api.amazon.com/auth/o2/token
POST https://api.amazon.com/auth/o2/token
clientid and clientsecret - You get these credentials after you register your application. Refer to Viewing your application information and credentials for more information.
refresh_token - You get your LWA refresh token from Seller Central after authorizing your application.
Request Body
[{"name"=>"grant_type", "value"=>"refresh_token", "datatype"=>"string"}, {"name"=>"refresh_token", "value"=>"{{refresh_token}}", "datatype"=>"string"}, {"name"=>"client_id", "value"=>"{{client_id}}", "datatype"=>"string"}, {"name"=>"client_secret", "value"=>"{{client_secret}}", "datatype"=>"string"}]