I bought a beast and brought me a code to have three months free of apple music but the code does not work for me.

Hi Y02ovalles,
Thanks for using the Apple Support Communities. I'm a bit unclear on exactly what you are describing, but if you've never had Apple Music before and would like to try it out, you should be able to click on the "Free Trial" button in the center or upper right hand corner of the following page to set up a three month trial:
Apple Music - Apple

On the other hand, if you are saying that you have purchased or received a 3-month Apple Music Gift Card and are having issues redeeming it, you may find the information and troubleshooting steps outlined in the following articles more helpful:

Redeem App Store & iTunes Gift Cards, Apple Music Gift Cards, and content codes - Apple Support
If you can't redeem your App Store & iTunes Gift Card, Apple Music Gift Card, or content code - Apple Support
Regards.