Describe the bug

1. Zebedee callback does not mark the invoice as completed because confirmedAt field is not set

To Reproduce
Steps to reproduce the behavior:

1. Configure Zebedee as payments processor and configure callback settings
2. Receive a callback for a paid invoice from Zebedee
3. Look at the error in the logs and notice that invoice isn't marked as paid

Expected behavior

1. Invoice should be confirmed
2. Relay sends out event confirming payment has been received

Logs
If applicable, attach log messages showing the bug and context when the bug happened.

Additional context
Add any other context about the problem here.