Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires phpspec/prophecy dev-master as 1.19 -> satisfiable by phpspec/prophecy[dev-master]. - phpspec/prophecy dev-master requires php ^7.2 || 8.0.* || 8.1.* || 8.2.* || 8.3.* -> your php version (8.4.0-dev) does not satisfy that requirement. Problem 2 - Root composer.json requires phpspec/prophecy-phpunit dev-master#0604e27 as 2.2.1 -> satisfiable by phpspec/prophecy-phpunit[dev-master]. - phpspec/prophecy dev-master requires php ^7.2 || 8.0.* || 8.1.* || 8.2.* || 8.3.* -> your php version (8.4.0-dev) does not satisfy that requirement. - phpspec/prophecy-phpunit dev-master requires phpspec/prophecy ^1.18 -> satisfiable by phpspec/prophecy[1.19 (alias of dev-master), 1.x-dev (alias of dev-master)]. - phpspec/prophecy 1.19 is an alias of phpspec/prophecy dev-master and thus requires it to be installed too. - phpspec/prophecy 1.x-dev is an alias of phpspec/prophecy dev-master and thus requires it to be installed too.