Try using the twitch-cli to test your callback https://github.com/twitchdev/twitch-cli/blob/main/docs/event.md#verify-subscription
And/or visiting your callback URL yourself to test it works as expected.
Try using the twitch-cli to test your callback https://github.com/twitchdev/twitch-cli/blob/main/docs/event.md#verify-subscription
And/or visiting your callback URL yourself to test it works as expected.