CAWI bulk survey link delivery

Hi everyone:

I am implementing bulk delivery of CAWI survey links. After creating the assignments, Survey Solutions indicates the total number of assignments created. Then, after sending invitation links, Survey Solutions indicates the number of invitations successfully sent. I realize that not all the assignments created are successfully sent with the links. My challenge is that I am unable to identify which assignments were not delivered to survey participants. Does someone know a way to identify these failed invitations in Survey Solutions? Thanks.