When you purchase Mixcraft directly from Acoustica or from a retailer - it comes with a retrieval code. The retrieval code is redeemed HERE.
Entering the retrieval code triggers our system to send you a registration code via email. If you've already done this, there is no need to ever do it again. You need to keep and re-use the registration code, not the retrieval code.
If you didn't keep your registration email/code, get it resent here.