If you've already decided which bundle you want to buy, download any plugin from this bundle, open it in your favorite DAW, press the “REGISTER” button there and collect your ID number. Then come back here, to the "Buy now" page and enter your ID into the matching ID text box (for instance, if you want to get the bundle that includes "Callisto VSTi", then enter your ID into the "MAX!"bundle's ID text box). Once you added the ID, press "BUY NOW" and complete the purchase. Once the purchase is complete, you'll get the serial immediately in the "serial number" textbox and the details of the purchase as well as a matching serial number will also get sent to your Email. Copy the serial number from here or from your Email, go back to the opened plugin in the DAW, paste it tinto the serial number text box and press "save". Once at least one plugin is registered, the entire bundle becomes registered as well