To assign extensions to users, you must first create a pool of extensions. Extensions are numbers that identify users within your phone system. You can create a pool of extensions by specifying a range of numbers that are available for assignment. You can then assign extensions to users individually or in bulk from the Users page in Genesys Cloud CX Admin. Reference: https://help.mypurecloud.com/articles/create-a-pool-of-extensions/ https://help.mypurecloud.com/articles/assign-extensions-to-users/