Error installing composer require spatie/laravel-webhook-client

[UdyW]

I'm trying to install this package in a Lumen project.
composer require spatie/laravel-webhook-client

But I'm getting the error;

  [InvalidArgumentException]                                                                                           
  Package spatie/laravel-webhook-client at version  has a PHP requirement incompatible with your PHP version (7.1.23)  

My composer.json;

{
"name": "laravel/lumen",
"description": "The Laravel Lumen Framework.",
"keywords": ["framework", "laravel", "lumen"],
"license": "MIT",
"type": "project",
"require": {
"php": ">=7.1.3",
"dusterio/lumen-passport": "^0.2.15",
"laravel/lumen-framework": "5.8.*"
},
"require-dev": {
"fzaninotto/faker": "^1.4",
"phpunit/phpunit": "^7.0",
"mockery/mockery": "^1.0"
},
"autoload": {
"classmap": [
"database/seeds",
"database/factories"
],
"psr-4": {
"App\": "app/"
}
},
"autoload-dev": {
"classmap": [
"tests/"
]
},
"scripts": {
"post-root-package-install": [
"@php -r "file_exists('.env') || copy('.env.example', '.env');""
]
},
"config": {
"preferred-install": "dist",
"sort-packages": true,
"optimize-autoloader": true
},
"minimum-stability": "dev",
"prefer-stable": true
}

[UdyW]

I have fixed this by adding

    "platform": {
        "php": "7.3"
    }

in to the config section of the composer.jason file.