@avinashmurthy you are right that this cURL command translates to what you tried, checked in Convert curl commands to JavaScript .
fetch('https://<dunzo_host>/api/v1/token', {
headers: {
'client-id': '<CLIENT_ID>',
'client-secret': '<CLIENT_SECRET>',
'Accept-Language': 'en_US',
'Content-Type': 'application/json'
}
});
But I would try adding those client properties to the body anyway.