Talk users in NIPR environment

Nextcloud Talk 13.0
CentOS 7

We have been successful on our network with video, audio and screen sharing with a handful of users. We send a link out to users to join a meeting. However if users are in a NIPR environment they can only do the chat. They cannot hear audio, see video or see screen sharing. Everyone else can hear and see everything. The common thing seems to be users being on a NIPR environment. Any thoughts as to why those users have problems?

No idea about NIPR, but do you have a TURN server?

Does this have anything to do with P2P? Does a STUN or TURN server need to be set up in this situation? Is this because Nextcloud Talk needs to know a users public address?

No no TURN server.