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You only created a new contribution. To submit it for actual validation, you need to create a new revision on the page for your contribution. Please keep in mind that extensions do need to get validated by the extensions team, and that might take a bit of time. We try to validate everything within a...

As said before, you will need to get the raw post data, and decode that yourself. You cant use the phpBB request class as that requires you sending normal post data.

phpBB doesnt parse the json automatically that is send via POST. You will need to get the raw POST data and use json_decode on that data