I bought the "VEGAS Movie Studio 16 Suite Platinum". However, I did not receive the activation code for "Trasition 5 Ultimate"
"VEGAS Movie Studio 16 Suite comes with Titler Pro 7 Express (along with the template packs) and the Supreme Package (Transitions 5 Ultimate, Cartoonr Plus, Chroma Key Pro, and Essentials 5 Volume 3).
For the Suite version customers should only have to install and activate TP7 Express and the Supreme Package."
There are the Platinum and Suite versions but no "Suite Platinum".
I bought the "VEGAS Movie Studio 16 Suite Platinum". However, I did not receive the activation code for "Trasition 5 Ultimate"
Where you bought it from? if from MAGIX than look at your e-mail "Confirmation of your order from Magix" scroll there to find NewBlue Transitions 5 Ultimate SN.
The OP has Suite or Platinum, not "Suite Platinum".
In the VMS 16 Suite version the Transitions pack is part of the file NewBlue Supreme Package. The Serial Number for this will also activate your Transitions.
In the VMS 16 Platinum version you do need the Serial Number for the Transitions pack. In case you actually have the Platinum version, follow the advice given by FayFen. Check also your email spam folder if you bought the download version (or the package material if you bought the physical version).