If you are unable to connect to SightCall in an integrated environment (Salesforce, Zendesk, etc.) and are getting stuck at "has already been taken" status, then that means the login ID (commonly email address) used in your integrated environment somehow has already been taken or used in the SightCall platform.
This issue typically occurs when you have multiple tenants in SightCall platform such as PROD, UAT, DEV; and your login ID has been used in UAT or DEV while you're trying to connect to PROD tenant.
To fix this issue, please first reach out to the SightCall administrator on your company so they can correct the issue for you. If you need further assistance, contact SightCall support.