SOLVED: Digital Post: Some transactions are failing using "Digital Post"

We have received reports that transactions are failing using the "Digital Post" integration.

The issue is now considered resolved. 

Events Time and date
Reports are coming in. 10:00 AM 23rd of September
Troubleshooting started 10:00 AM 23rd of September
Internal developers are reported 13:26 PM 23rd of September
Issue is fixed 16:33 PM 23rd of September