WordPress: fix “Updating failed. The response is not a valid JSON response” (GARMTECH hosting)

The WordPress message “Updating failed. The response is not a valid JSON response” usually appears when the editor (Block Editor / Gutenberg) cannot communicate with WordPress REST API.

Step 1 — Quick checks (most common fixes)

1. Reload and try again (temporary cache/CDN issues happen).
2. Open the REST API URL in your browser:
   https://your-domain.tld/wp-json/
   You should see JSON text. If you get a 403/404/500 or HTML output, the REST API is blocked or broken.
3. Clear caches:
   • Browser cache (or test in Incognito/Private mode)
   • LiteSpeed Cache (LSCache) plugin → Purge All
   • Cloudflare/CDN cache (if you use it)

Step 2 — Re-save permalinks

1. In WordPress go to Settings → Permalinks.
2. Click Save Changes (even if you change nothing).

Step 3 — Disable conflicting plugins/themes

Security and cache plugins are the most common cause. Temporarily disable:

• Security plugins (firewall/WAF)
• Caching/optimization plugins (if you use more than LSCache)
• Any recently installed plugin

Then test editing a page again.

Step 4 — Check SSL and site URL settings

• Make sure your admin panel opens on HTTPS without redirect loops.
• Verify the WordPress Site Address (URL) and WordPress Address (URL) are correct.

Step 5 — Check server logs in Plesk

If the REST API URL returns an error, check logs to find the exact reason:

1. Open Plesk for your hosting plan.
2. Go to Websites & Domains → Logs.
3. Look for entries around the time you reproduce the problem.

Step 6 — Consider PHP limits (if requests time out)

If updates fail due to timeouts, increase PHP limits (memory, execution time) for the domain in Plesk.

After the fix

• Re-enable plugins one by one to find the exact conflict.
• Keep WordPress core, themes, and plugins up to date.