Your requirements could not be resolved to an installable set of packages. Problem 1 - mantle-framework/testkit[v0.12.2, ..., v0.12.3] require symfony/http-foundation ^6.0.20 -> satisfiable by symfony/http-foundation[v6.0.20, ..., 6.4.x-dev]. - mantle-framework/testkit v0.12.9 requires nunomaduro/collision ^6.0 || ^7.0 -> found nunomaduro/collision[dev-develop, v6.0.0, ..., 6.x-dev (alias of dev-develop), v7.0.0, ..., v7.x-dev] but it conflicts with your root composer.json require (^5.0). - symfony/http-foundation[v6.0.0-BETA1, ..., 6.0.x-dev] require php >=8.0.2 -> your php version (8.0; overridden via config.platform, actual: 8.1.27) does not satisfy that requirement. - symfony/http-foundation[v6.1.0-BETA1, ..., 6.4.x-dev] require php >=8.1 -> your php version (8.0; overridden via config.platform, actual: 8.1.27) does not satisfy that requirement. - mantle-framework/testkit[v0.12.4, ..., 0.12.x-dev] require nunomaduro/collision ^6.4 -> found nunomaduro/collision[dev-develop, v6.4.0, 6.x-dev (alias of dev-develop)] but it conflicts with your root composer.json require (^5.0). - Root composer.json requires mantle-framework/testkit ^0.12 -> satisfiable by mantle-framework/testkit[v0.12.2, ..., 0.12.x-dev].