Could not find package with stability dev in a version installable using your PHP version When I want to install Drupal Commerce using Composer via Git Bash terminal and using the following command:

$ composer create-project drupalcommerce/project-base mystore --stability dev


I get the following error:


  [InvalidArgumentException]   Could not find package
  drupalcommerce/project-base with stability dev in a version
  installable using your PHP version 5.6.40.
  
  create-project [-s|--stability STABILITY] [--prefer-source]
  [--prefer-dist] [--repository REPOSITORY] [--repository-url
  REPOSITORY-URL] [--dev] [--no-dev] [--no-custom-installers]
  [--no-scripts] [--no-progress] [--no-secure-http] [--keep-vcs]
  [--remove-vcs] [--no-install] [--ignore-platform-reqs] [--]
  [] [] []


So what can I do?
The package that triggers the error is  drupalcommerce/project-base. If you check the composer information for that package you see: 

  "require": {
        "php": "&gt;=7.0.8",
        "ext-curl": "*",
        "composer/installers": "^1.2",
        "cweagans/composer-patches": "^1.6.5",
        [...]


As you see, it requires PHP 7.0.8 or higher. You have PHP 5.6.40. You should upgrade your PHP, not only because this package but also because PHP 7.x is much faster and PHP 5.6 is not recommended anymore, not to forget that PHP 5.6 end of life was hit a year ago, on the beginning of 2019.