Process completed with exit code 127.

Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires silverstripe/installer 4.11.x-dev -> satisfiable by silverstripe/installer[4.11.x-dev]. - silverstripe/framework[4.11.16, ..., 4.11.x-dev] require guzzlehttp/guzzle ^7 -> found guzzlehttp/guzzle[7.0.0-beta.1, ..., 7.9.x-dev] but it conflicts with your root composer.json require (^6.3). - silverstripe/installer 4.11.x-dev requires silverstripe/recipe-cms 4.11.x-dev -> satisfiable by silverstripe/recipe-cms[4.11.x-dev]. - silverstripe/recipe-cms 4.11.x-dev requires silverstripe/recipe-core 4.11.x-dev -> satisfiable by silverstripe/recipe-core[4.11.x-dev]. - silverstripe/recipe-core 4.11.x-dev requires silverstripe/framework 4.11.x-dev -> satisfiable by silverstripe/framework[4.11.x-dev].

symfony/thanks contains a Composer plugin which is blocked by your allow-plugins config. You may add it to the list if you consider it safe. You can run "composer config --no-plugins allow-plugins.symfony/thanks [true|false]" to enable it (true) or disable it explicitly and suppress this exception (false) See https://getcomposer.org/allow-plugins