Creates a new webhook subscription. The signing secret is returned once in the response.
Merchant API key: ak_live_* (production) or ak_test_* (sandbox).
HTTPS endpoint URL.
"https://api.example.com/webhooks/anton"
1payout.created, payout.approved, payout.processing, payout.sent, payout.completed, payout.failed, payout.cancelled, payout.returned, beneficiary.created, beneficiary.updated, beneficiary.deleted, batch.uploaded, batch.completed, batch.failed, balance.low, funding.credit, screening.hit, fx.quote.created, fx.exchange.created, fx.exchange.completed, fx.exchange.failed, test Subscription created with signing secret.