The README says the agent requires Python 2.6+ However, it appear that the syntax used in the code is not compatible with Python 3.
The first thing it blows up on when you try to run with Python 3 is the except syntax (https://portingguide.readthedocs.io/en/latest/exceptions.html#the-new-except-syntax)
Output from the logs when Python 3.9.0 is used:
File "/apps/rollbar-agent/venv/rollbar-agent", line 321
except Exception, e:
^
SyntaxError: invalid syntax
Please update documentation to clarify python version requirements.