In order to enter alphanumeric caller names you need to use your system keyboard. Please tap above the number keypad to activate it.
Info: SecTel.io caller names (=VoIP user names) are 6 digit alpha-numeric small case. - E.g. "abc456"
Tap the green "call" icon to initiate calls.
Wait for call to be established and key exchange to finalize. You may want to compare the passwords with the other calling party to verify the encryption channel is end-to-end with no man in the middle.
(If there was a man in the middle he would need to decrypt and re-encrypt to cheat the system, as we allow only encrypted calls. In case of re-encrypting, he wouldn´t be able to achieve the use the same encryption keys again, and as a result of that the shown "human readable key hash" would differ)