Firstly, the collected digits field will not be populated in the CTI Events from AES unless the VDN is "monitored" by some device - So you can use IDS or Voice mediastore to do this.

Secondly, the monitored VDN needs to the VDN the call is DELIVERED to, AFTER the collected digits have been added, NOT the VDN in which you are adding the digits. (As you have already received the delivered event for this VDN before you added the digits)

Lloyd