Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires friendsofphp/php-cs-fixer ^2.16||^3.0 -> satisfiable by friendsofphp/php-cs-fixer[v2.16.0, ..., v2.19.3, v3.0.0, ..., v3.40.0]. - phpunit/phpunit[8.5.12, ..., 8.5.28] require phpspec/prophecy ^1.10.3 -> satisfiable by phpspec/prophecy[v1.10.3, ..., v1.17.0]. - phpunit/phpunit[7.4.0, ..., 7.5.20] require php ^7.1 -> your php version (8.3.0) does not satisfy that requirement. - sebastian/diff[3.0.0, ..., 3.0.2] require php ^7.1 -> your php version (8.3.0) does not satisfy that requirement. - phpunit/phpunit[8.5.0, ..., 8.5.11] require php ^7.2 -> your php version (8.3.0) does not satisfy that requirement. - phpspec/prophecy[1.11.0, ..., 1.11.1] require php ^7.2 -> your php version (8.3.0) does not satisfy that requirement. - phpspec/prophecy[v1.10.2, ..., v1.10.3] require php ^5.3|^7.0 -> your php version (8.3.0) does not satisfy that requirement. - phpspec/prophecy[1.12.0, ..., 1.13.0] require php ^7.2 || ~8.0, <8.1 -> your php version (8.3.0) does not satisfy that requirement. - phpspec/prophecy[1.14.0, ..., v1.15.0] require php ^7.2 || ~8.0, <8.2 -> your php version (8.3.0) does not satisfy that requirement. - phpspec/prophecy[v1.16.0, ..., v1.17.0] require php ^7.2 || 8.0.* || 8.1.* || 8.2.* -> your php version (8.3.0) does not satisfy that requirement. - phpunit/phpunit[8.5.29, ..., 8.5.34] require sebastian/diff ^3.0.2 -> satisfiable by sebastian/diff[3.0.2, 3.0.3, 3.0.4]. - Conclusion: don't install sebastian/diff 3.0.4 (conflict analysis result) - Root composer.json requires phpunit/phpunit ~7.4||~8.5 -> satisfiable by phpunit/phpunit[7.4.0, ..., 7.5.20, 8.5.0, ..., 8.5.34].