A UUID needs to be represented by a 32 bit hexadecimal format - you can find out more about this here.
M can only be 1, 2, 3, 4, or 5
N can only be 8, 9, A, or B
To generate your own UUID:
If you are using a Mac, you can open up Terminal, and then type uuidgen and click enter. This will generate a valid UUID for you.
Visit create.passkit.com, click on the ‘Lock Screen’ tab on top, click on ‘Beacon Details’, and simply type in a name in the name field (i.e. My Beacon). This will automatically generate a UUID.
For more information on the format of a UUID, please see this Wikipedia article.