Thank you for your interest in Talkatone.
The root certificate on your device has expired. This certificate allows you to access Talkatone and other apps & services on your android devices. This certificate is not exclusive to Talkatone. However, we can help you correct this issue.
1. Your Android device will need to have a PIN set otherwise by default you can not install any certificates to the device. This is found under Settings->Security->Screen Lock
2. Click here to download Comodo RSA Certification Authority
3. Open your device settings menu.
4. Scroll down to Security>Install from Storage/SD Card>Downloads(locate the comodorsacertificationauthority.crt file)
5. Tap the file & Type a name for the certificate.
6. Tap OK. (If you haven't already set a PIN, pattern, or password for your phone, you’ll be asked to set one up.)
7. Restart the Talkatone app and you should be able to connect.
We hope this information helps you out.
NOTE: These instructions may be slightly different from device to device.
*If you would like to learn more about this matter we encourage you to view the following article.