Your requirements could not be resolved to an installable set of packages. Problem 1 - nette/application[v3.1.11, ..., v3.1.x-dev] require nette/http ^3.0.2 -> found nette/http[v3.0.2, ..., v3.3.x-dev] but it conflicts with your root composer.json require (^4.0.0). - nette/application[dev-master, v3.2.x-dev] require nette/http ^3.3 -> found nette/http[v3.3.x-dev] but it conflicts with your root composer.json require (^4.0.0). - nette/application 4.0.x-dev is an alias of nette/application dev-master and thus requires it to be installed too. - Root composer.json requires nette/application ^3.1.11 || ^4.0.0 -> satisfiable by nette/application[v3.1.11, ..., v3.2.x-dev, 4.0.x-dev (alias of dev-master)].