Boomi HTTP Client Connector with OAuth 2.0 for Acquia DAM is not Working

Question

Ideally Boomi is capable to generate Application Access Token with different inbuilt connectors like salesforce, google, etc. Since Acquia DAM is not supported with inbuilt connector; i have to generate Application Access Token manually in HTTP client Connection; Authorization code is generated smoothly with out any issues & Boomi is able to acknowledge receival of authorization code; But further part of this communication viz. generating Access Token using Authorization Code is not working where Boomi is returning error of Error attempting to retrieve Auth Access token. java.io.IOException: Server returned HTTP response code: 503 for URL: https://api.widencollective.com/2/oauth/access-token

I am using HTTP Client Connector with OAuth 2.0 Authentication Type & Authorization Code as Grant type for generating Application Access Token in Boomi for further API operation between Systems.

I followed exactly what is mentioned in Boomi Documentation regarding OAuth 2.0 Settings & I am using Authorization Parameter for redirect_uri for callback of authorization code & generating access token from it.

1. Tried updating "Authorization Parameter"
2. Tried updating "Access Token Parameter"