 API keys, test mode toggle, etc. Type: Action hook (dynamic) When Fired: When customer submits payment through gateway Parameters: Invoice object, payment amount Purpose: Process the payment and handle response from gateway API Return: Should update invoice payment ledger with transaction details Type: Action hook (dynamic) When Fired: When gateway sends webhook notification of payment Parameters: Raw request body and headers from gateway Purpose: Verify webhook signature and update payment status Security: Must verify signature to prevent spoofed payments