If you’re talking about the farmOS Crop Plan module, specifically, then I wonder if you are running into this known issue:
Tl;dr: it isn’t currently possible to create plan_record entities via the API.
This thread has some good general information about the crop plan data model, as well as a link to that issue, and a temporary workaround that you can use to patch the issue for now. We still need to come up with a proper long-term fix.
I’m curious what issues you ran into with “reading” data… that should work normally. But it is important to understand how the crop plan models things. It uses a plan entity (of bundle crop) to represent the plan itself, and then it uses plan_record entities (of bundle crop_planting) that connects the plan to individual asset entities (of bundle plant). The plan_record also contains some metadata about that relationship, which is specific to the plan, including planned seeding date (seeding_date), expected days to transplant (transplant_days), expected days to maturity (maturity_days), and expected harvest window (harvest_days). These represent the “planned” or “expected” lifecycle of each plant asset… but the plant asset itself, and the logs associated with it, represent the “actual”.
More information about the crop plan module in general, if you haven’t seen it, is here: