Describe how Telegram calls work.

[pistolbz]

I think it works through a peer-to-peer setting, it's not okay to have each other's contacts. In Telegram Settings -> Privacy... -> Calls -> Peer-to-Peer, both the recipient and the listener must set Peer-to-Peer depending on the current relationship type such as Everybody, Contacts or Nobody to receive get the corresponding target IP address.

Telegram notes that: "Disabling peer-to-peer will relay all calls through Telegram servers to avoid revealing your IP address, but may decrease audio and video quality."

This explanation will help everyone better understand why the tool is not working as expected and how to make it work. This is a great tool.

[theblackhole]

I just want to add something to what you said: by default the setting is "Contact".

(I think that's why @n0a stated "you must be in each other's contacts.")