Glad to hear that you're planning to give us a call. I think we should be able to clear up any questions you have regarding this over the phone. If you continue to have any trouble with the integration for your client, please let me know and I'll be happy to provide additional support.
If you haven't called yet, here is the number:
Stamps.com Support: Toll-free 1-888-434-0055, Monday - Friday, 6 a.m. - 6 p.m. Pacific Time.