21473: Transfer target AccountSid is not related to the phone number owner

This error occurs when you try to transfer a phone number by updating AccountSid on an IncomingPhoneNumber, but the destination account is not in the same parent and subaccount hierarchy as the account that currently owns the number. You can only transfer phone numbers between your main account and its subaccounts, or between subaccounts under the same main account.

• The target AccountSid belongs to a different account hierarchy instead of the phone number owner's parent account or a sibling subaccount under the same main account.
• The target AccountSid is neither the current owner's parent account nor a child account of that same parent.
• The transfer request uses an unrelated Twilio account SID instead of an account that is connected through subaccounts.

• Verify that the source account and destination account are in the same account hierarchy before retrying the transfer. Use the account relationship information to confirm that the destination is the main account or a subaccount under the same main account.
• Retry the transfer only to your main account, one of its subaccounts, or another subaccount under the same main account.
• Send the transfer as an HTTP POST to the IncomingPhoneNumber instance resource and set AccountSid to the valid destination account SID.
• Use your main account credentials when you submit the transfer request.

• IncomingPhoneNumber resource
• REST API: Subaccounts
• REST API: Accounts