How to retrieve the string (GUID) a.k.a. Entitlement ID

Hello,
I'm implementing a simple application to license HL and SL keys interfacing to EMS web service.

Program is actually working, but I would like to store in a text file some information of the generated entitlement, and in particular mode I would like to store the EID that can be used to search in EMS the related entitlement.

I'm not able to find any way to get the EID back. How can I retrieve it? I tried to create an entitlement in draft status, and EID is already present. In EMS web service documentation is several times stated that the entId is an integer and EID is a string:

This is different from the Entitlement ID string. Example: entId - 10 (integer);
Entitlement ID (or EID): gd5f6vfg-y57f-he55-3r5d7w9g7tx3 (string).

But the question is: where can I retrieve the EID?

Thanks in advance,
Stefano