What values for the php variables are shown in the admin area of your site ("Information" - "Server" section on PHP tab) and/or on the "Server analysis" tab of the iZAP Videos plugin settings page?

The analysis tab of the iZAP Videos plugin should display all relevant variables. The values displayed there should be the values also in effect when processing uploaded videos.

For a start (and to find out if any limits might cause the problem) I suggest to test it by uploading a very small videos. For example, the video included in the server_test subfolder within the iZAP Videos plugin folder could be used.

I'm not fully convinced the problem is with php variables though. The error message would indicate that the upload action call could not be authenticated correctly. But this authentification should be within the code of the IZAP Videos plugin for sure. So, the question is if maybe some other plugin interferes (so, another test could be to test with all other 3rd party plugins temporarily disabled).

Or does the analysis tab displays any other issues? There should be only successes shown. Otherwise, some component is missing on the server or is not correctly configured.

The variables in the Server information are also the default, they just don't appear to change whatever I do with php.ini or .htaccess. I also had an error uploading a smaller video, this gave a different error. I will do what you suggest and disable all other plugins and see if we have interference as I have installed other plugins after the video plugin, thank you for your assistance.

Seeing the path in the PHP log line I think you are running PHP as FastCGI module (php-fpm). In this case you can't set PHP variables via .htaccess files. The values set there are simply ignored. And maybe the php.ini file location as displayed by Elgg (/etc/php.ini) is also not the php.ini actually used by php-fpm! You would need to figure out if there might be another php.ini (e.g. /etc/php7/fpm/php.ini - or at some other location) where you could configure the limits used by PHP, Elgg and iZAP Videos.

What was the different error when uploading the smaller video? Maybe there's a second issue apart from setting the PHP variable values to larger values.

In you Bootstrap.php file:

use Elgg\DefaultPluginBootstrap;

class Bootstrap extends DefaultPluginBootstrap {

  public function activate() {
    $path = "path/to/your/db/script.sql";
    _elgg_services()->db->runSqlScript($path);
  }

}

The SQL file will be called on each plugin activation.

Thanks a lot.

please keep in mind "_elgg_services()" is an internal function and changes can be made without the need for backwards compatibility.

Why do you need to run a SQL script? Can't it be solved with the existing methods like an async upgrade?