Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires composer/composer ^2.8.9 -> satisfiable by composer/composer[2.8.9]. - Root composer.json requires estahn/phpunit-json-assertions ^4.0 -> satisfiable by estahn/phpunit-json-assertions[v4.0.0]. - composer/composer 2.8.9 requires justinrainbow/json-schema ^6.3.1 -> satisfiable by justinrainbow/json-schema[6.3.1, 6.4.0, 6.4.1, 6.4.2]. - estahn/phpunit-json-assertions v4.0.0 requires justinrainbow/json-schema ^5.0 -> satisfiable by justinrainbow/json-schema[5.0.0, ..., 5.3.0]. - You can only install one version of a package, so only one of these can be installed: justinrainbow/json-schema[5.0.0, ..., 5.3.0, 6.0.0, ..., 6.4.2]. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.