202 means that Twitch accepted the sub request, and will then asynchronously call your callback URL to verify it, and complete setup of the subscription.
You need to check if your callback is being called, and if you are correctnyl sending back the challenge
And then if the subscription is enabled in Get EventSub Subscriptions - Reference | Twitch Developers
This may suggest that your webhook_url has invalid SSL or is not web accessable, hence no data. But check if your subscription is enabled
I suspect, that since you are using ngrok you didn’t challenge response correctly.