Eloqua OAuth2.0

Question

I want to use Eloqua's OAuth2.0. When I try to use it with "authorization_code" grant type it fails when generating accessToken and refreshToken with following error

{
    "error": "invalid_grant",
    "error_description": "The authorization code is incorrect, malformed, expired, or has been invalidated."
}

I am following steps at: https://docs.oracle.com/en/cloud/saas/marketing/eloqua-develop/Developers/GettingStarted/Authentication/authenticate-using-basic-auth.htm

Steps I followed:

Hit following url: https://login.eloqua.com/auth/oauth2/authorize?response_type=code&client_id=my-client-id&redirect_uri=https://www.google.com/&scope=full&state=xyz

I signed in using my creds and accepted the request

It then redirected to: https://www.google.com/?code=some-eloqua-server-side-generated-code&state=xyz

Then using postman I made the following request:

curl --location 'https://login.eloqua.com/auth/oauth2/token' \
--header 'Content-Type: application/json' \
--header 'Authorization: Basic base64-encoded-value-of-clientId:clientSecret-string' \
--header 'Cookie: culture=en-US' \
--data '{
    "grant_type":"authorization_code",
    "code":"some-eloqua-server-side-generated-code",
    "redirect_uri":"https://www.google.com/"
}'

Anyone can help me with what could be the possible problem in my steps or the Eloqua OAuth2.0 just does not work(atleast with authorization_code grant_type)

I even did not see "invalid_grant" error anywhere in Eloqua's documentations.