Laravel 5.2: The Process class relies on proc_open, which is not available on your PHP installation

After many weeks of trying to resolve this error. The following fixes worked

1. Upgrade project from Laravel 5.2 to 5.4
2. On CPanel using "Select Php version" set PHP version to 7
3. Or on CPanel using "MultiPHP Manager" set PHP version to ea-php70

Now, cron job runs smoothly. I hope this helps someone.

Laravel 6 and higher (proc_open Error)

It is because of Flare error reporting service enabled in debug mode There is a workaround for this.

Publish flare config file php artisan vendor:publish --tag=flare-config

and in config/flare.php

Set

'collect_git_information' => false 
'reporting' => [
     'anonymize_ips' => true,
     'collect_git_information' => false,
     'report_queries' => true,
     'maximum_number_of_collected_queries' => 200,
     'report_query_bindings' => true,
     'report_view_data' => true,
],

For me removing cached version of config.php file solve problem(Laravel 6). go to bootstrap/cache/config.php and remove file. Also don't forget to change APP_URL to your domain address. PHP version should be as required by laravel version.

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for shared host if you can't change php.ini, you should use laravel 5.8.