Your requirements could not be resolved to an installable set of packages. Problem 1 - Root composer.json requires amphp/amp ^3.1.1, found amphp/amp[v3.1.1] but the package is fixed to v2.6.5 (lock file version) by a partial update and that version does not match. Make sure you list it as an argument for the update command. Problem 2 - Root composer.json requires amphp/parallel ^2.3.2, found amphp/parallel[v2.3.2] but the package is fixed to v1.4.4 (lock file version) by a partial update and that version does not match. Make sure you list it as an argument for the update command. Use the option --with-all-dependencies (-W) to allow upgrades, downgrades and removals for packages currently locked to specific versions.