I'm getting '401 Unauthorized' error on GetAccessTokenWithAuthCode. No issues when using Permanent Key to communicate with AdobeSign.

Steps performed:

Prerequisites - API Applications created in Adobe; Site Properties and Consumed REST API URLs set in AdobeSignConnector 

1. Click on Authorize (for OAuth) on Home screen

2. Redirected to Adobe, and got the request to Sign in the account and click on 'Allow Access'

3. Once clicked, application goes to RedirectScreen and nothing else is shown. (code & state is appended in URL)

4. A check in Adobe Access Tokens show no access tokens granted

Errors:

1. Service Center shows the following error:

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401 Unauthorized
   at ssAdobeSignConnector.CcAdobeSignOAuth.ActionGetAccessToken(HeContext heContext, ICcAdobeSignOAuthCallbacks _callbacks, String inParamgrant_type, String inParamclient_id, String inParamclient_secret, String inParamredirect_uri, String inParamcode, STGetAccessTokenResponseStructure& outParamResponse)

401 Unauthorized
at ssAdobeSignConnector.CcAdobeSignOAuth.ActionGetAccessToken(HeContext heContext, ICcAdobeSignOAuthCallbacks _callbacks, String inParamgrant_type, String inParamclient_id, String inParamclient_secret, String inParamredirect_uri, String inParamcode, STGetAccessTokenResponseStructure& outParamResponse)
at ssAdobeSignConnector.Actions.ActionAdobe_GetAccessTokenWithAuthCode(HeContext heContext, String inParamsessionCode, String& outParamtokenType, String& outParamtoken, String& outParamError, String& outParamErrorDescription)
at ssAdobeSignConnector.ScreenServices.AdobeSignConnector_MainFlow_RedirectScreen_Controller.<ActionAdobe_GetAccessTokenWithAuthCode>b__1(HeContext heContext, String screenName, JObject screenModel, JObject inputParameters, JObject clientVariables)
   at OutSystems.RESTService.Controllers.ScreenServicesApiController.endpoint(String input, String endpointName, String apiVersion, EndpointImplementationDelegate implementation)

Adobe_GetAccessTokenWithAuthCode
System.Exception: 401 Unauthorized
at Object.s [as getException] (https://sebhqoutdevsrv.sarawakenergy.com.my/AdobeSignConnector/scripts/OutSystems.js?eq9LGmzdgJbMq6dbNoVMvQ:2:10241)
at c.onSuccess (https://sebhqoutdevsrv.sarawakenergy.com.my/AdobeSignConnector/scripts/OutSystems.js?eq9LGmzdgJbMq6dbNoVMvQ:3:6706)
    at XMLHttpRequest.<anonymous> (https://sebhqoutdevsrv.sarawakenergy.com.my/AdobeSignConnector/scripts/OutSystems.js?eq9LGmzdgJbMq6dbNoVMvQ:3:2122)

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2. Request / Response seen from dev tools