The environment name you provide will be used as the domain name. For example: If you provide Contoso' as the environment ...

The environment name you provide will be used as the domain name. For example: If you provide ‘Contoso' as the environment name, the login URL for the environment will be https://contoso.operations.dynamics.com. Also, make sure this is a meaningful domain name, for example: contoso-dev, contoso-test, contoso etc. The environment name must be three or more characters in length. Once the environment has been deployed, the same name cannot be used for any other environment since the domain name needs to be unique.