Facebook Instant Games: Must Not Call Private APIs

Question

Upon uploading to Facebook Instant Games we got the error "Must Not Call Private APIs: Games must use the Instant Games SDK properly and should not call private methods directly."

We are using the same set of publicly documented functions found in the Quickstart, and have greped the build output for offenders, revealing nothing. No documentation. No hits on the internet. AI has no idea.

Next steps?

Answer 1

Through a long game of submitting chunks of code through FB servers for validation (binary search), the problem was a parent.postMessage call in the Svelte runtime function add_iframe_resize_listener.

I'll leave it as an exercise for reader to decide what to do about it. Hopefully this saves someone a day of their lives to go drink on a beach instead.