Your requirements could not be resolved to an installable set of packages. Problem 1 - gammamatrix/playground dev-develop requires ext-intl * -> it is missing from your system. Install or enable PHP's intl extension. - gammamatrix/playground 73.x-dev is an alias of gammamatrix/playground dev-develop and thus requires it to be installed too. - Root composer.json requires gammamatrix/playground dev-develop|dev-master|^73.0 -> satisfiable by gammamatrix/playground[dev-develop, 73.x-dev (alias of dev-develop)]. To enable extensions, verify that they are enabled in your .ini files: - /usr/local/etc/php/conf.d/docker-php-ext-sodium.ini You can also run `php --ini` in a terminal to see which files are used by PHP in CLI mode. Alternatively, you can run Composer with `--ignore-platform-req=ext-intl` to temporarily ignore these required extensions.