On desktop: 

After the issue has occurred: 

In the conversation list:

1. Click Settings .
2. Click Options.
3. Click Save the calling debug report.
4. Send it to Support.

OR 

Go to the menu bar (not in Wire for web):

     1. Click Help.

     2. Click Download Debug Logs.

     3. Send it to Support.

On Mobile

After the issue has occurred: 

In the conversation list:

1. Tap your Profile in the upper left corner.
2. Tap  Settings.
3. Tap Advanced.
4. Tap Create debug report.

Please describe briefly what went wrong to help us to identify the issue.

Calling logs do not include: any call content, personal information, fingerprint, device ID, user ID, or IP address.

Please be aware: Logs are off by default on Android. Please turn on Collect usage data in Advanced. Only then, data will be collected and stored on your device. As soon as you turn off the toggle all saved data will be deleted.