Problem Overview A commonly encountered error while attempting to obtain an OAuth token from Salesforce using the authorization code flow. After receiving an authorization code: https://login.salesforce.com/services/oauth2/token Including the following parameters: code grant_type = “authorization_code” redirect_uri client_id client_secret However, Salesforce responded with: {"error":"invalid_grant","error_description":"authentication failure"} HTTP status code 400 accompanied the error—indicating that despite all parameters being provided, the token exchange failed unexpectedly. Step-by-Step to Fix Authentication The comprehensive approach to resolve this issue: Create a Salesforce Developer Account Begin with a free developer account from developer.salesforce.com. Set Up a Connected App From the Setup menu, navigate to Create → Apps → Connected Apps → New . Fill out required fields—including OAuth settings and callb...