The connection can not be established. What can I do?

Threema calls don’t work properly if there are certain kinds of network restrictions.

  • If you use security measures like a firewall, antivirus software, an ad blocker, or a VPN , please make sure that Threema is excluded from their activities.
  • Make sure that you are not connected to the guest profile of the local Wi-Fi router; many routers do not allow certain connections for guests.
  • If you have only tried one network, please attempt to make a call using a different network (e.g. cellular data).
  • If the problem only occurs when calling specific contacts, please check their verification level. When calling contcats of the verification level 1 (red), calls are routed through the Threema server to disguise the IP addresses. In rare cases, this may lead to connectivity issues. Therefore, increase the verification level by scanning the contact’s QR code or using the contact synchronization.
  • If you use one or both of the following options, please deactivate them to try if that resolves the issue: 
    • “Threema > Settings > Threema Calls > Always realy calls”
    • “Threema > Settings > About Threema > Troubleshooting > IPv6 for calls and web” (Android), respectively “Threema > Settings > Advanced > IPv6” (iOS).