License usage is shown in the cluster management console of Dynatrace Managed. It's also split per environments. Does this satisfy your requirements?
Actually, that not generally possible since app infrastructure can be shared between several apps. (at least for host unit licenses).
For RUM I can imagine this is doable (sum of user sessions), but I;m not sure this metric is exposed using API.
For synthetic it is simple math.
Currently, the best approach would be to have separate environment per application.
I have the same issue.
Speaking about licences consumed by hosts, you can use this API https://www.dynatrace.com/support/help/dynatrace-a... , collecting the attribute "consumedHostUnits" .
But, for sessions consumed per tenant or application, no API exists. I have so created a RFE to which you can subscribe https://answers.dynatrace.com/spaces/482/dynatrace...
. So it may be available before the end of this year.