10/06/2020 4:33pm NZT - This issue appears to be resolved and all affected messages have been resent earlier this afternoon.
Our mail service provider, Sendgrid, are currently reporting service disruption issues which may prevent some emails from sending from Invoxy.
You can keep an eye on their current status here - https://status.sendgrid.com/
Once the incident is resolved, the Invoxy team will identify any messages that were affected by the outage and automatically resend them for you - you don't need to do anything.