This is another compelling feature of OIC3, making it simple for you to see the number of billed messages per integration and get notified about such. For example you can set a threshold and get informed via email when that threshold has been reached.
I have the following simple integration that processes a large payload, large is relative, but, in my case, it's well over the 50kb limit for 1 billable message.
I run this 3 times in the tester and check the instance metrics in the OCI console -
Let's hone in on the Received Messages metric -
Now to the Billable or Consumed messages metric -