Docs for all releases
Account can not be added, same IP / Name exists within other client message appears during adding new IP to an account.
Added IP can already exist in the VCS.
Check where the same IP exists in the VCS: you can do it using the Advanced Search in the top right corner of the section. After you find where the same IP is specified, you need to check its parameters. Adding is possible if different protocols / voip gateways / tech prefixes or type (origination of termination) are selected for each account. After you identify each account with different parameters, try to add new IP again.