For simplicity, the Provider is using the main trunking number as the identifier.
It needs to be set for both SIP registrations and SIP Invites.
The next step of the bank teller is to check the account and ensure that the person requesting the withdrawal is entitled to complete that transaction.
Perhaps you are allowed to withdraw up to $1,000, but no more. Just having a successful authentication does not prove entitlement.
An easy solution to this problem is using a SIP Profile with CUBE and replacing the 4 digit number with the 10 digit Pilot Number (this is same number in your sip-ua portion of the router config).