Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires roave/better-reflection ^6.54.0 -> satisfiable by roave/better-reflection[6.54.0]. - roave/better-reflection 6.54.0 requires nikic/php-parser ^5.4.0 -> found nikic/php-parser[v5.4.0] but it conflicts with your root composer.json require (^4.19.4). Problem 2 - Root composer.json requires psalm/plugin-phpunit ^0.19.2 -> satisfiable by psalm/plugin-phpunit[0.19.2]. - psalm/plugin-phpunit 0.19.2 requires vimeo/psalm dev-master || ^6 -> found vimeo/psalm[6.0.0, ..., 6.4.0] but it conflicts with your root composer.json require (^5.26.1). Problem 3 - Root composer.json requires roave/infection-static-analysis-plugin ^1.36.0 -> satisfiable by roave/infection-static-analysis-plugin[1.36.0]. - roave/infection-static-analysis-plugin 1.36.0 requires vimeo/psalm ^6.0 -> found vimeo/psalm[6.0.0, ..., 6.4.0] but it conflicts with your root composer.json require (^5.26.1). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.