hmm, not sure, what version 0.8.1 is. Note, that this thread is 1.5 years old. i don't think, there is such a version, although there was a 0.81).
There are two stable version in addition to the head version:
a) one in the branch oacs-5-3 (named 0.60.6)
b) one in the branch oacs-5-4 (named 0.106.1)
The head version is currently 0.109
Where did you get your version from?
Most likely, you have in your error.log an earlier error message which is the cause for the symptom that the method get_payload is not defined.
