The HTTP 415 error occurs when a web server refuses a request due to an unsupported media type, often caused by a mismatch between the format expected by the server and what the browser sends. This can happen in various scenarios on WordPress installations, including working with REST API requests, form submissions, or file uploads. To resolve the issue, it's essential to check request headers, plugin/theme compatibility, file validation, and server configuration to ensure that the correct media type is being sent and recognized by the server. By identifying and addressing these potential causes, users can troubleshoot and fix the HTTP 415 error on their WordPress website.