How can I fix this sitemap error?

Hello,

I’m sorry to hear about the sitemap error you are facing on your websites. To resolve the "XML declaration allowed only at the start of the document" issue, you can follow these steps:

1. Check for Plugin Conflict:

   • Use the Health Check plugin to identify any conflicts caused by plugins. Deactivate all plugins except Rank Math and check if the issue persists.

2. Add Filter to Theme’s rank-math.php File:

   • If removing whitespace and cache didn’t work, you can add a filter to your theme’s rank-math.php file to disable sitemap caching. Here’s how:
     • Navigate to WordPress Dashboard → Tools → Theme File Editor or WordPress Dashboard → Appearance → Theme File Editor.
     • Choose the rank-math.php file and add the following filter:

       add_filter( 'rank_math/sitemap/enable_caching', '__return_false');

     • Save the changes and clear your website cache.

3. Confirm Sitemap Functionality:

   • After applying the changes, check your sitemap using an XML Sitemap validator to ensure the error is resolved.

If these steps do not resolve the issue, please feel free to reach out to our support team directly here for further assistance. We are here to help you with any additional support you may need.

Thank you for your patience and understanding. If you have any more questions or need further assistance, please let us know.

Sources:
Rank Math Sitemap Issues and Their Fixes » Rank Math
How to Fix "Incorrect HTTP Header Content-Type" Error in Sitemaps » Rank Math