SupportSync requires an Endicia ELS account. This is an account that can communicate with the Endicia Label Server (ELS).
A normal Endicia account doesn't have an account number and cannot be used with SupportSync or other services that use Endicia's API to create shipping labels.
Use this link to signup for an ELS account that will work with SupportSync:
Basic is the type of account needed. The Advanced plan allows consolidator carriers such as DHL Ecommerce UPS mail innovations.