Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires brick/varexporter ^0.4.0 -> satisfiable by brick/varexporter[0.4.0]. - brick/varexporter 0.4.0 requires nikic/php-parser ^4.0 -> found nikic/php-parser[v4.0.0, ..., v4.18.0] but it conflicts with your root composer.json require (^5.0.0). Problem 2 - vimeo/psalm[5.15.0, ..., 5.18.0] require nikic/php-parser ^4.16 -> found nikic/php-parser[v4.16.0, v4.17.0, v4.17.1, v4.18.0] but it conflicts with your root composer.json require (^5.0.0). - Root composer.json requires vimeo/psalm ^5.15 -> satisfiable by vimeo/psalm[5.15.0, 5.16.0, 5.17.0, 5.18.0]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.