Problem 1 - phpunit/phpunit[6.0.0, ..., 6.5.14] require php ^7.0 -> your php version (8.1.4) does not satisfy that requirement. - Root composer.json requires phpunit/phpunit ~6.0 -> satisfiable by phpunit/phpunit[6.0.0, ..., 6.5.14].

i try to run old laravel app, my php v is 8.1 so cannot run composer update ,install ,

composer install --ignore-platform-reqs

it also not work , my composer json file

{
    "name": "laravel/laravel",
    "description": "The Laravel Framework.",
    "keywords": ["framework", "laravel"],
    "license": "MIT",
    "type": "project",
    "require": {
        "php": "^7.0||^8.1.4",
        "coingate/coingate-php": "^2.0",
        "fideloper/proxy": "~3.3",
        "hesto/multi-auth": "^2.0",
        "intervention/image": "^2.4",
        "laravel/framework": "5.5.*",
        "laravel/tinker": "~1.0",
        "nwidart/laravel-modules": "^2.7",
        "stripe/stripe-php": "^6.0"
    },
    "require-dev": {
        "filp/whoops": "~2.0",
        "fzaninotto/faker": "~1.4",
        "mockery/mockery": "~1.0",
        "phpunit/phpunit": "~6.0",
        "symfony/thanks": "^1.0"
    },
    "autoload": {
        "classmap": [
            "database/seeds",
            "database/factories"
        ],
        "psr-4": {
            "App\": "app/",
            "Modules\": "Modules/"
        }
    },
    "autoload-dev": {
        "psr-4": {
            "Tests\": "tests/"
        },
        "files" :["app/Http/helpers/helpers.php"]
    },
    "extra": {
        "laravel": {
            "dont-discover": [
            ]
        }
    },
    "scripts": {
        "post-root-package-install": [
            "@php -r \"file_exists('.env') || copy('.env.example', '.env');\""
        ],
        "post-create-project-cmd": [
            "@php artisan key:generate"
        ],
        "post-autoload-dump": [
            "Illuminate\Foundation\ComposerScripts::postAutoloadDump",
            "@php artisan package:discover"
        ]
    },
    "config": {
        "preferred-install": "dist",
        "sort-packages": true,
        "optimize-autoloader": true
    }
}

how can i fix this issue,

  Problem 1
    - phpunit/phpunit[6.0.0, ..., 6.5.14] require php ^7.0 -> your php version (8.1.4) does not satisfy that requirement.
    - Root composer.json requires phpunit/phpunit ~6.0 -> satisfiable by phpunit/phpunit[6.0.0, ..., 6.5.14].