Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires sonsofphp/cookie-contract 0.3.x-dev (exact version match), found sonsofphp/cookie-contract[dev-main, 0.3.x-dev (alias of dev-main)] but these were not loaded, likely because it conflicts with another require. Problem 2 - Root composer.json requires sonsofphp/http-handler-contract, it could not be found in any version, there may be a typo in the package name. Problem 3 - Root composer.json requires sonsofphp/http-message 0.3.x-dev (exact version match), found sonsofphp/http-message[dev-main, 0.3.x-dev (alias of dev-main)] but these were not loaded, likely because it conflicts with another require. 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.