[x-license] improve v9 license key version mismatch error guidance

Author: aemartos

docs/public/_redirects

@@ -8,6 +8,8 @@
 # should all be prefixed with x-
 
 /r/x-get-license https://mui.com/pricing/ 302
+/r/x-license-account https://mui.com/store/account/licenses/ 302
+/r/x-license-key-upgrade https://support.mui.com/hc/en-us/articles/26762005295516-How-can-I-generate-a-v9-license-key 302
 /r/x-license-eula https://mui.com/legal/mui-x-eula/ 302
 /r/x-license-annual https://mui.com/legal/mui-x-eula/#annual-license 302
 /r/x-license-trial https://mui.com/x/introduction/licensing/#evaluation-trial-licenses 302

packages/x-license/src/Watermark/Watermark.tsx

@@ -57,6 +57,11 @@ function Watermark(props: WatermarkProps) {
       }}
     >
       {getLicenseErrorMessage(licenseStatus.status)}
+      {process.env.NODE_ENV !== 'production' && (
+        <div style={{ fontSize: 12, letterSpacing: 1, marginTop: 8 }}>
+          Open the browser console for details on how to resolve this.
+        </div>
+      )}
     </div>
   );
 }

packages/x-license/src/utils/licenseErrorMessageUtils.ts

@@ -63,10 +63,12 @@ export function showLicenseKeyVersionMismatchError() {
   showError([
     'MUI X: License key version mismatch.',
     '',
-    'The license key you are using is not compatible with the version of the MUI X packages installed.',
-    'This happens when using a license key from a previous major version (e.g. a v8 license with v9 packages).',
+    'The license key you are using was issued for an older major version of MUI X (e.g. a v8 license with v9 packages installed).',
+    'Each major version uses a different license key format, so the key needs to be regenerated — your existing license is not lost.',
     '',
-    'To resolve this, you can either get an new license key at https://mui.com/r/x-get-license or from your account profile at https://mui.com/store/account/licenses/, or downgrade to an older MUI X version that matches your current license key.',
+    'To resolve this, you can either:',
+    '- Generate a new key compatible with the installed version from your account at https://mui.com/r/x-license-account (free for existing customers, the new key inherits your current expiration date). More details at https://mui.com/r/x-license-key-upgrade.',
+    '- Or downgrade the MUI X packages to the major version that matches your current license key.',
   ]);
 }