Originally Posted by
AutoSlash
Sixt does not support the passing of loyalty numbers from third parties, however, as of a few weeks ago, the email address is now being passed so you can access and manage it directly on Sixt's website as well as check-in online. In fact, as soon as you make a new booking through us, you will receive an email from Sixt with online check-in instructions now.
I just made one yesterday actually and I get the same error on Sixt's website when I tried to access it. I also didn't get the referenced email from Sixt about the reservation. I've emailed their support desk to see if they can add it but no reply yet.
That one was from the Autoslash website (or Autoslash cover of Priceline) vs. Priceline itself.