If you’ve ever tried to connect Salesforce to an external API, whether it’s a payment gateway or your company’s internal system, you’ll need to provide an API key, a Bearer token, or a custom header such as X-Calling-User or X-Billing-Code.
That “something extra” is what we call a custom header, and in this tutorial, you will understand exactly how to set one up in Salesforce using Named Credentials and External Credentials step by step, no Apex code required.