PS4 party problems?

For me, when I play with some friends, I have the problem that I don't hear them and they don't hear me. It is definitely not the headset because otherwise we both hear everyone else in the party and they also hear us.

Then there's always a sign and it flashes all the time.

You were mute, weren't you? It seems like?

Could be due to the NAT type, go to settings, then on the Internet connection, then test on the Internet connection and then there must be a 2 for the NAT type. 1 and 3 is bad. 1 is bad because your router can get a virus more easily, with 3 your router blocks everything so it blocks it. At 2 your router is secure and you can play normally. Your colleague should do the same.