Problem:
Adding comment to to record by simply create WORKLOG mbo through the rest Api is not possible.
Such action results in Error 400: comlog#ownerNull.
Solution:
Right way to do this is adding WORKLOG from parent record, using custom object structure (which has to have relation to WORKLOG enabled).
Tasks:
1. Choose (or create) Object Structure for Integration, which will have relation to WORKLOG object.
2. Fetch record using that object structure
3. Add workload in form of attributes list:
WORKLOG.index.DESCRIPTION
(…) where index will be number of existing comments + 1