The WordPress ‘Invalid response code’ error occurs when the server returns a response that cannot be properly processed by WordPress. This typically happens when the server sends malformed responses, incorrect HTTP status codes, or when there are issues with JSON parsing. The error disrupts communication between your WordPress site and the server, causing failures in various operations including content updates, plugin functionality, and admin panel actions. These issues often stem from server configuration problems, plugin conflicts, or communication breakdowns between the client browser and server.