Optional to use Guzzle:
composer require "guzzlehttp/promises"Optional to use ReactPhp:
composer require "react/promise"Guzzle: Overblog\PromiseAdapter\Adapter\GuzzleHttpPromiseAdapter
ReactPhp: Overblog\PromiseAdapter\Adapter\ReactPromiseAdapter
To use a custom Promise lib you can implement Overblog\PromiseAdapter\PromiseAdapterInterface