Your requirements could not be resolved to an installable set of packages. Problem 1 - payum/core[1.7.0, ..., 1.7.3] require php-http/client-implementation ^1.0 -> could not be found in any version, but the following packages provide it: - symfony/http-client Provides powerful methods to fetch HTTP resources synchronously or asynchronously - php-http/discovery Finds and installs PSR-7, PSR-17, PSR-18 and HTTPlug implementations - php-http/guzzle6-adapter Guzzle 6 HTTP Adapter - php-http/guzzle7-adapter Guzzle 7 HTTP Adapter - php-http/curl-client PSR-18 and HTTPlug Async client with cURL - symfony/symfony The Symfony PHP framework - kriswallsmith/buzz Lightweight HTTP client - php-http/mock-client Mock HTTP client - php-http/socket-client Socket client for PHP-HTTP - php-http/react-adapter React HTTP Adapter - php-http/guzzle5-adapter Guzzle 5 HTTP Adapter - voku/httpful A Readable, Chainable, REST friendly, PHP HTTP Client - jorge-matricali/http-client A wrapper of libcurl that implements PSR-7 HTTP message interface. - php-http/buzz-adapter Buzz HTTP Adapter - juststeveking/http-slim A slim psr compliant http client to provide better interoperability. - prestashop/module-lib-guzzle-adapter Plug modules to the Guzzle client available on a running shop - swisnl/php-http-fixture-client Fixture client for PHP-HTTP - php-http/cakephp-adapter CakePHP adapter for PHP-HTTP - code-tool/curl-client cURL client - code-tool/socket-client Socket client for PHP-HTTP ... and 39 more. Consider requiring one of these to satisfy the php-http/client-implementation requirement. - Root composer.json requires payum/core ^1.7 -> satisfiable by payum/core[1.7.0, 1.7.2, 1.7.3]. Potential causes: - A typo in the package name - The package is not available in a stable-enough version according to your minimum-stability setting see <https://getcomposer.org/doc/04-schema.md#minimum-stability> for more details. - It's a private package and you forgot to add a custom repository to find it Read <https://getcomposer.org/doc/articles/troubleshooting.md> for further common problems.