I just bought a number of Magix products through a promo at Fanatical.
The one I wanted to use was Music Maker. It came with serial numbers for Moviemaker Coupon 1 and Moviemaker Coupon 2. These two serial numbers begin with G3. There was not serial number for Music Maker. It needs a P3 serial number.
The version included in the Fanatical bundle is the free version which does not need a serial number. I guess as it is claim the value is "£49.99" the value of the two coupons must be this.