This means that you're trying to register an event
odk-instance-first-load in the form which is not supported by commcare. You can check this event by opening the form xml(follow this link for reference) and searching for
We only support the following events in commcare:
I'm not sure about the meaning of this custom action that you're trying to use. I'm guessing it means that you wanna trigger something when the form loads for the first time? If that's the case, you can replace all occurences of
xforms-ready that'd give you the same outcome.
Otherwise, another way to fix the issue is to edit the source xml of form and remove all events using