[SalesForce] OAuth2 token request failing

My access token request is failing with the following error response in HTTP Response.

{
error: "invalid_client_id"
error_description: "client identifier invalid"
}

I am trying with the Username-Password flow for OAuth.

I am testing with "Advanced REST Client" in Chrome.

This is my payload

https://login.salesforce.com/services/oauth2/token&grant_type=password&client_id=3MVG9ZL0ppGP5UrDhLqebweqGDkIkyGQRjYkfWtLLSwKDal0AhSWZIG7EU7gsYQn4JjfCt.SOoBrJLmyEpslT&clientSecret=7217724494220744623&username=apiuser1982@gmail.com&password=qazwsx123UKBZb1SEA3LgCcptvGBb8ibpk

All my credentials are correct and I am stuck.

My connected app settings (Client Key/Secret) are also right without any typos and such.

Can someone help as to what could be wrong ?