The Signal messenger and protocol.

A few days ago I tried to add a contact to Signal. The other person is already a user as none of us can find the other on the network.

On my side, I get a message that the number is still not on Signal, while on the other side the network returns an "unknown error" message when searching for my contact.

What may be causing issues, although it makes no sense for me:

• I'm an Android user, while the other phone is an iPhone
• we're from different countries, including different continents, with an ocean apart

Another person, on that same country, has already added my number to their Signal on an Android phone, as well as another number from my country.

This makes no sense whatsoever to me.

Any thoughts?