Twilio is used for SMS operator notifications, phone number collection for compliance, and 1-confirmation redemptions on cash-out transactions.
To configure, first sign up for a Twilio account.
During signup, you'll verify your personal phone number. (This won't be the number used for sending, rather, Twilio will assign you a new number dedicated to outgoing messages.)
Once confirmed and logged into the dashboard, click 'Get a number'. Ensure that you choose a number that is capable of SMS (not all are).
Then upgrade your account by adding payment information, adding funds, and turning on automatic recharge.
IMPORTANT: Enable Geo Permissions for all countries or those you expect your customers' numbers to primarily be from.
Copy down your 'Account SID', 'Auth Token', and new phone number from the Twilio main console page.
Enter the credentials in the Twilio panel of the admin under 'Third party services'.
The From number (Twilio number) is the phone number you purchased from Twilio.
The To number (Notifications number), is your personal number for when/if you enable SMS notification.
Both must be filled in, and in international format (+, followed by the country code, followed by the number).
See this artlce to enable SMS notifications.
See this article to configure SMS compliance.
See this article to configure SMS for cash-out.