Matomo for WordPress 5.13.0: HTTP 500 – is_plugin_active() undefined after Hostinger migration

WordPress Plugin
1

Matomo for WordPress: fatal Call to undefined function is_plugin_active() after hosting migration

Hi,

After migrating a WordPress site from Hostinger Cloud Professional to Hostinger Agency hosting, Matomo for WordPress stopped working correctly.

Environment:

  • Matomo for WordPress 5.13.0
  • WordPress
  • PHP 8.4.24
  • nginx / Hostinger
  • Site migrated on 29 August 2026

Initially, tracking requests to:
/wp-content/plugins/matomo/app/matomo.php
returned HTTP 500.

Changing Endpoint for HTTP Tracking API to WP REST API fixed the tracking endpoint:
/wp-json/matomo/v1/hit/

However, Matomo Reporting still returns HTTP 500 when loading:
/wp-content/plugins/matomo/app/index.php

The PHP error log shows:

PHP Fatal error: Uncaught Error: Call to undefined function is_plugin_active() in wp-content/plugins/matomo/app/bootstrap.php:166

For the tracking endpoint the same fatal occurred via:
app/matomo.php -> app/piwik.php -> app/bootstrap.php

For Reporting:
app/index.php -> app/bootstrap.php

bootstrap.php successfully finds and loads wp-load.php; ABSPATH is defined. It subsequently reaches:

if ( !is_plugin_active('matomo/matomo.php') ... )

at line 166, but is_plugin_active() is not defined in that direct-request context.

The site otherwise works normally.

Is this a known issue with the direct Matomo bootstrap, PHP 8.4, nginx, symlinked hosting environments, or Hostinger? Is there a recommended fix that does not involve modifying Matomo core files?

2

Hello @Don_t_Panic Thanks for providing the detailed error information.

Since the issue started after migrating to the new Hostinger environment, this appears to be related to how direct PHP requests are handled on the new server.

Could you please check the following:

  • Try temporarily switching from PHP 8.4 to PHP 8.3 to see if the issue persists.
  • Check whether the new hosting environment uses symlinks or a different WordPress document root/path.
  • Check for any Hostinger-specific MU plugins or server configurations that could affect direct PHP requests under /wp-content/plugins/.
  • Compare the nginx/PHP-FPM configuration with the previous hosting environment, if possible.
  • Check Matomo Analytics > Diagnostics > System Report for any warnings related to paths, symlinks, or PHP.

We wouldn’t recommend modifying Matomo’s bootstrap.php directly, as any changes could be overwritten by future updates.