Si intentando instalar Horizon en Laravel tenemos el siguiente error:

Your requirements could not be resolved to an installable set of packages.

Problem 1
– laravel/horizon v4.3.3 requires ext-pcntl * -> the requested PHP extension pcntl is missing from your system.
– laravel/horizon v4.3.2 requires ext-pcntl * -> the requested PHP extension pcntl is missing from your system.
– laravel/horizon v4.3.1 requires ext-pcntl * -> the requested PHP extension pcntl is missing from your system.
– laravel/horizon v4.3.0 requires ext-pcntl * -> the requested PHP extension pcntl is missing from your system.
– laravel/horizon 4.x-dev requires ext-pcntl * -> the requested PHP extension pcntl is missing from your system.
– Installation request for laravel/horizon ^4.3 -> satisfiable by laravel/horizon[4.x-dev, v4.3.0, v4.3.1, v4.3.2, v4.3.3].

Installation failed, reverting ./composer.json to its original content.

Una vez comprobado que tenemos el módulo instalado procederemos a instalar Horizon con el siguiente comando:

composer require laravel/horizon --ignore-platform-reqs

Y posteriormente podemos seguir con los pasos:

php artisan horizon:install

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