Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires drupal/acquia_cms_headless dev-develop -> satisfiable by drupal/acquia_cms_headless[dev-develop]. - drupal/acquia_cms_headless dev-develop requires drupal/next ^1.6 -> satisfiable by drupal/next[1.6.0, 1.6.1, 1.6.2, 1.6.3]. - drupal/next[1.6.0, ..., 1.6.3] require drupal/core ^9 || ^10 -> found drupal/core[9.0.0-alpha1, ..., 9.5.x-dev, 10.0.0-alpha1, ..., 10.4.x-dev] but it conflicts with your root composer.json require (11.0.x-dev). Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.