Hi,
Once you’ve connected to the Bedrock server of CubeCraft, you’ll see a giant birthday cake in the main lobby. Normally this shouldn’t be hard to find as it’s situated right in front of the spawn point. All you gotta do in order to claim the free pack is click on that cake.
Here’s a small GIF I created to show how it’s done:
Hopefully, this helped you out. If not, feel free to let us know by replying to this thread.