Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires sylius/sylius ~1.11.0 -> satisfiable by sylius/sylius[v1.11.0, ..., v1.11.15]. - sylius/sylius[v1.11.0, ..., v1.11.15] require sylius/calendar ^0.3 -> found sylius/calendar[v0.3.0] but it conflicts with your root composer.json require (^0.5.0).