[SalesForce] Session expired or invalid

I am trying to build Salesforce to Salesforce integration using Named Credentials.

Followed steps from below blog.

http://www.jitendrazaa.com/blog/salesforce/salesforce-to-salesforce-integration-using-named-credentials-in-just-5-lines-of-code/

• Created Connected App in destination org
• Created Authorization Provider in source org

• Defined Named Credential in source org.

  HttpRequest feedRequest = new HttpRequest();
  
  feedRequest.setEndpoint('callout:Dev3Org/services/data/v32.0');
  
  feedRequest.setMethod('GET');
  
  Http http = new Http();
  
  HTTPResponse feedResponse = http.send(feedRequest);
  

When I ran above code in Source Org (anonymous window) then am getting below error

Session expired or invalid