here's the error when installing

[Sirgalas]

problem 1
- Installation request for phpmongokit/yii2-mongo-odm dev-master -> satisfiable by phpmongokit/yii2-mongo-odm[dev-master].
- phpmongokit/yii2-mongo-odm dev-master requires sokil/php-mongo 1.* -> satisfiable by sokil/php-mongo[1.0.17, 1.1.1, 1.10.10, 1.11.0, 1.11.1, 1.11.2, 1.11.3, 1.11.4, 1.11.5, 1.11.6, 1.11.7, 1.12.0, 1.12.1, 1.12.2, 1.12.3, 1.12.4, 1.12.5, 1.12.6, 1.12.7, 1.12.8, 1.13, 1.13.1, 1.13.2, 1.13.3, 1.13.4, 1.13.5, 1.13.6, 1.13.7, 1.13.8, 1.13.9, 1.14, 1.15, 1.15.1, 1.15.2, 1.16, 1.16.1, 1.17, 1.18.1, 1.18.2, 1.19, 1.19.1, 1.19.2, 1.2.5, 1.20, 1.21, 1.21.1, 1.21.2, 1.21.4, 1.21.5, 1.22, 1.22.1, 1.22.2, 1.3.3, 1.4.1, 1.5.0, 1.6.3, 1.7.0, 1.8.5, 1.9.0] but these conflict with your requirements or minimum-stability.

[sokil]

Show your composer.json please. Minimum stability by default is stable but you try to add dev-master version of phpmongokit/yii2-mongo-odm.

[sokil]

Also if you install library in php7, there are some requirements. I have add description to README.