Why are contacts not added to my list when I use the listAddContacts method -Benchmark Email

Knowledge Base Home aero-right API Why are contacts not added to my list when I use the listAddContacts method?

Why are contacts not added to my list when I use the listAddContacts method?

Some of the common reasons why the contacts are not added to the list would be:

The contact has not clicked on the confirmation email. You can check this by clicking on the "Not Opted-in Yet" link in the contact listing
The contact could be in your Master Unsubscribe List
The contact could be already present in your list