There are three possible explanations for this error:
- The other party didn’t generate a key pair.
- The other party may have a private key but hasn’t pushed their public key to the server. You may ask them to push it.
- You may need to add the receiver’s public key manually to send them encrypted message. Ask them to send you their public key as an email attachment. When received, just tap on the public key attachment. The public key will be automatically added to the local keystore. After that, you can send encrypted messages to this person.