The "Beta Middleware Used" error occurs if you are using Middleware in a version of Next.js prior to v12.2. The Middleware feature was still in beta in those versions and not yet covered by semver or Semantic Versioning rules.

Despite this error, you can continue using Middleware in versions prior to v12.2. Be aware that upgrading to newer versions of Next.js will require changes to your application to accommodate updates in Middleware handling.

If you're using Next.js on Vercel, your existing deployments using Middleware will remain functional, and you can keep deploying your site with Middleware. However, when you decide to upgrade your site to Next.js v12.2 or later, you'll need to follow the provided upgrade guide to ensure compatibility.

• Middleware Upgrade Guide - Learn more about the necessary steps to upgrade your application to a version of Next.js that includes the official version of Middleware.