Payouts go via Stripe Connect. You need to onboard your Stripe Connect account once:
1. Open Affiliate in the sidebar.
2. Under "Payouts" click Connect with Stripe.
3. Go through the Stripe onboarding: bank details, identity, possibly VAT number.
4. After completion, you see a green ✓ Connected badge.
From that moment on, your available commissions are automatically transferred monthly (around the 15th) to your linked bank account.