Yes, for the inventory control you will need to use IPN. We can Help you add this in a Premiere ticket.
there are 3 types of support incidents that we offer:
1) Free - For dealing with installation and supported usage issues.
2) Premium - For expedited assistance
3) Premiere - For custom coding
the initial incident type you purchased was a premium incident type, for assistance with custom coding, you will need to upgrade the incident you purchased to a premier incident type.