The digital signing is experiencing issues. Signable (the third-party digital signing company) has been reporting errors today (24 December 2023), so they appear to be experiencing difficulties. Their status page can be checked at https://status.signable.co.uk. In addition, there seems to be an issue with Signable notifications, and we are investigating if that is connected to the Signable troubles.
Please monitor the Signable status page and try submitting for signing again when that's clear. We will also continue to monitor and update here when appropriate.