Q: composer cannot install knp menu bundle in symfony 3.4 I tried to install the knp-menu-bundle in Symfony 3.4 but I got the following error:
$ composer require knplabs/knp-menu-bundle dev-master
[InvalidArgumentException]
Package knplabs/knp-menu-bundle at version dev-master has a PHP requirement incompatible with your PHP version (5.5.9)
It's odd because my PHP version is 7.1 and not 5.5.9.
Updating my post to show my composer.json.
{
    "name": "symfony/framework-standard-edition",
    "license": "MIT",
    "type": "project",
    "description": "The \"Symfony Standard Edition\" distribution",
    "autoload": {
        "psr-4": {
            "AppBundle\\": "src/AppBundle",
            "CarBundle\\": "src/CarBundle"
        },
        "classmap": [ "app/AppKernel.php", "app/AppCache.php" ]
    },
    "autoload-dev": {
        "psr-4": { "Tests\\": "tests/" },
        "files": [ "vendor/symfony/symfony/src/Symfony/Component/VarDumper/Resources/functions/dump.php" ]
    },
    "require": {
        "php": ">=5.5.9",
        "doctrine/doctrine-bundle": "^1.6",
        "doctrine/orm": "^2.5",
        "incenteev/composer-parameter-handler": "^2.0",
        "sensio/distribution-bundle": "^5.0.19",
        "sensio/framework-extra-bundle": "^5.0.0",
        "symfony/monolog-bundle": "^3.1.0",
        "symfony/polyfill-apcu": "^1.0",
        "symfony/swiftmailer-bundle": "^2.6.4",
        "symfony/symfony": "3.4.*",
        "twig/twig": "^1.0||^2.0"
    },
    "require-dev": {
        "sensio/generator-bundle": "^3.0",
        "symfony/phpunit-bridge": "^3.0"
    },
    "scripts": {
        "symfony-scripts": [
            "Incenteev\\ParameterHandler\\ScriptHandler::buildParameters",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::buildBootstrap",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::clearCache",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installAssets",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::installRequirementsFile",
            "Sensio\\Bundle\\DistributionBundle\\Composer\\ScriptHandler::prepareDeploymentTarget"
        ],
        "post-install-cmd": [
            "@symfony-scripts"
        ],
        "post-update-cmd": [
            "@symfony-scripts"
        ]
    },
    "config": {
        "platform": {
            "php": "5.5.9"
        },
        "sort-packages": true
    },
    "extra": {
        "symfony-app-dir": "app",
        "symfony-bin-dir": "bin",
        "symfony-var-dir": "var",
        "symfony-web-dir": "web",
        "symfony-tests-dir": "tests",
        "symfony-assets-install": "relative",
        "incenteev-parameters": {
            "file": "app/config/parameters.yml"
        },
        "branch-alias": {
            "dev-master": "3.4-dev"
        }
    }
}


A: Try just without dev-master below composer require knplabs/knp-menu-bundle "^2.0"
OR change:
 "require": {
        "php": ">=7.0",
        ...............


A: Issue is that knplabs/knp-menu-bundle requires the following:
"php": "^5.6 || ^7",

which you can see here. However your composer.json has:
"php": ">=5.5.9",

so you need to require at least 5.6 to make knp-menu-bundle dependency happy. Still you need to check if that's ok for all other dependencies as well.
