I have been sending my new recruits to join the newsletter so that they can get the exchange bonus pack. But about only half of them are getting the email with the code. And of the half that got the code, a few have told me that when they enter the code, it tells them that the code is invalid.

I have even made them recheck that they were entering the code right. And they double checked and said that they were.

If this a known issue? Or new? I didn't see a thread about here in the Problem & Bugs section.