Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires the-events-calendar/coding-standards dev-master -> satisfiable by the-events-calendar/coding-standards[dev-master]. - the-events-calendar/coding-standards dev-master requires wp-coding-standards/wpcs ^3.0.0 -> found wp-coding-standards/wpcs[3.0.0, 3.0.1] but it conflicts with your root composer.json require (^2.3). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.