DUO Telephony Credits are no longer available for purchase throught the MC Store. Please see the following directions to order Telephony Credits:

Purchasing DUO Telephony Credits

• Log into the DUO Admin console
  -Switch your account to the customer you need to purchase tokens for
• Select the Billing option on the left-hand menu
• Select Telephone Credits under the Billing sub-menu
• At the bottom of the screen, select the link to add a credit card (1x – the card is saved after entry)

Once this is complete, you’ll see an option to add credits:

• Enter the amount you want in 1,000 increments and click Purchase Credits button for both end users and Duo administrators.

Duo debits your telephony credit balance for each authentication call or SMS message sent (as per the rate card).

If you ever exhaust your telephony credit balance, your users will not be able to receive authentication phone calls or text messages. They will still be able to authenticate using non-telephony methods: Duo Push, Duo Mobile passcodes, and hardware tokens. Duo Push and Duo Mobile-generated passcodes — are app-based and have no telephony cost, but require a smartphone or other mobile device.

NOTE:  When using the DUO mobile app – Telephony credits are not needed. 

Link to addition Telephony Credit information here: https://duo.com/docs/telephony-credits