I personally never received a second email containing the code to activate my game beyond the early access. I had to follow these steps to find it and hope this helps someone else out:

1. Go to: https://www.findmyorder.com/DRHM/sto...E&Locale=en_US (U.S. link only)

2. Enter the information as asked, either email and last 5 of CC used, or order number and password.

3. Once logged in you should see your most recent purchase, which will hopefully be FFXIV ARR.
You will see the follwing towards the top:
Unlock Code: XXXXXXXXXXXXXX
Serial Number: XXXX XXXX XXXX XXXX XXXX <---- This is the code you want!
PC Digital Download
Electronic Download

4. Enter the serial in your mog station account by using add platform button.

Hope this helps!