Why do I get a "Call to undefined function activate_plugin()" error?

This is the most common error when you try to programmatically manage wordpress plugins outside of the normal admin context (like via WP-Cron, a custom REST API endpoint, or an AJAX call). The WordPress core does not load the file containing these administrative functions on the frontend to save memory. You must explicitly include it using require_once ABSPATH . 'wp-admin/includes/plugin.php'; before calling the function.

Can I programmatically manage wordpress plugins from the frontend?

Yes, mechanically speaking, you can execute the code from the frontend by including the necessary plugin.php file as described above. However, from a security standpoint, this is highly discouraged. Exposing plugin management logic to frontend requests opens massive security vulnerabilities. Any script that modifies active plugins should be strictly authenticated, require administrator capabilities, and ideally use nonces to prevent Cross-Site Request Forgery (CSRF) attacks.

What happens if a programmatically activated plugin has a fatal error?

If you pass a plugin to activate_plugins() and that plugin contains a syntax error or a fatal exception (like redeclaring a class), it will immediately halt your PHP execution. The WordPress function attempts to do a "sandbox" check by loading the plugin file, but it is not infallible. If a fatal error occurs during programmatic activation, it can sometimes leave the database in an inconsistent state or cause a White Screen of Death. You should always test plugin activations in a staging environment before automating them in production.

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