Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpunit/phpunit ^6, found phpunit/phpunit[6.0.0, ..., 6.5.14] but these were not loaded, because they are affected by security advisories ("PKSA-z3gr-8qht-p93v"). Go to https://packagist.org/security-advisories/ to find advisory details. To ignore the advisories, add them to the audit "ignore" config. To turn the feature off entirely, you can set "block-insecure" to false in your "audit" config. Problem 2 - yoast/phpunit-polyfills is locked to version 1.1.5 and an update of this package was not requested. - yoast/phpunit-polyfills 1.1.5 requires phpunit/phpunit ^4.8.36 || ^5.7.21 || ^6.0 || ^7.0 || ^8.0 || ^9.0 -> found phpunit/phpunit[4.8.36, 5.7.21, ..., 5.7.27, 6.0.0, ..., 6.5.14, 7.0.0, ..., 7.5.20, 8.0.0, ..., 8.5.52, 9.0.0, ..., 9.6.34] but these were not loaded, because they are affected by security advisories ("PKSA-z3gr-8qht-p93v"). Go to https://packagist.org/security-advisories/ to find advisory details. To ignore the advisories, add them to the audit "ignore" config. To turn the feature off entirely, you can set "block-insecure" to false in your "audit" config. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.