Sitemap error when using PHP8

Hello @jackyliao,

Thank you for contacting support.

That error comes from a constant that should be defined by WordPress by default but on your website is not being defined.

There are 2 ways to fix this issue:

1. You can define the constant FS_CHMOD_FILE in your wp-config.php file.
2. You can disable the caching from the sitemap by using the following filter: https://rankmath.com/kb/exclude-sitemaps-from-caching/#transient-cache

Hope this helps solve your issues.

Don’t hesitate to get in touch if you have any other questions.