I think there is no direct way to do this. Dynatrace is alerting on failures rate itself not about particular exception. There is no option in custom alert for this as well (at least I didn’t found it). But if this is exception it should be visible in process logs as well, am I right? If yes and you have log analytics license that is covering size of this log, you can alway create log based event:
In such case problem will be fired based on this.
The upcoming improvement of the custom events and alert configuration will allow you to define an alert on a custom service metric. A custom service metric could be defined to catch your specific error code and count those occurrence. The alert would then be sent out if the occurrence count is above your selected threshold.
As I mentioned this is an upcoming feature that you can request as a preview in Dynatrace release 176.
Hhhhhhmmmm..... I was just poking around trying to figure this one out myself. You are correct I believe. Event today on the latest release, I do not see anything dealing with exceptions in the "Custom event for alerting" under services. I have a team would had some exceptions under a service and would like to raise a problem when they are detected.
I was looking at "Error detection" and "Custom errors" under the service, but I am not confident that anything in there would trigger a problem based on an exception.