Retrieves the list of members in the specified Signing Group.
The external account number (int) or account ID GUID.
Optional. The ID of the signing group.
Note: When you send an envelope to a signing group, anyone in the group can open it and sign it with their own signature. For this reason, we recommend that you do not include non-signer recipients (such as carbon copy recipients) in the same signing group as signer recipients. However, you could create a second signing group for the non-signer recipients and change the default action of Needs to Sign to a different value, such as Receives a Copy.