One of the issues with Dynamics 365 Retail is the way the errors are displayed to end users. I have come across many instances where it becomes very difficult to investigate and get to the root cause of an error message. The lack of clarity becomes an issue when you are not very familiar with the functional/technical aspects of HQ and POS.
One of the many common errors I have seen is server side and database related issue as you can see in the below screen grab. Here the issue is with the loyalty card setup in payment methods. However the error message is not very clear in terms of where exactly the issue is.
I have seen similar error once when there was an issue with printing the receipt. The issue was with the design itself. When we redesigned the receipts while adhering to proper layout the error went away.
Hope this helps!