This issue has now been resolved. All users must update the CabCard app to the latest version (8.4.2, version code 49) in order to resume processing SoftPOS transactions.
To do so please visit the Google Play Store and tap the "Update" button (link: https://cab.link/cc-go)
We sincerely apologise for the disruption caused by today's incident, and will be conducting a root cause analysis with our SoftPOS vendor in due course to ensure this type of failure is prevented in future.