Requirements on PUID given to Trusted Service voice service

I’m making use of the Trusted Server flow to interact with Epic Online Service’s voice chat (note: not using Lobbies). As part of creating a chat room, it’s necessary to send a PUID (Product User ID) for each user. In the Trusted Server flow, this PUID is whatever arbitrary string we choose to use. Since there’s no user/login/auth backing of any kind within EOS that we’re using.

Question is: what requirements are there on that PUID?

Detail: For our first prototype implementation, I’m just creating rooms with 14 people named “a” through “n”, then assigning which of our users is which single-letter name, per voice room they join, as and when they request to join one.

But am I causing issues or hitting limits within EOS if PUID “a” is in too many voice rooms at once? Each PUID “a” in various voice rooms actually being used by a different player.

If so, I’m thinking I would instead generate a random UUID v4 in place of just “a” through “n”. To almost-guarantee uniqueness of PUIDs within our EOS product.