# Offline Processing

The RESTful API is designed to allow most merchants to connect directly to the data centers of Shift4.  However, depending on the devices or flows a merchant plans to use, an interface may need to send requests to a locally installed UTG in order to control the devices. Using a local UTG has another advantage -- the UTG software has a few capabilities that make it simple for your interface to support offline transaction processing when a merchant’s internet connection goes down.  **The following section applies only to those who are using locally installed UTGs.**

Offline mode mimics online transaction processing by locally tokenizing CHD and returning an ‘R’ (referral) response when a card is swiped, tapped, or manually entered. While offline, the merchant can use their backup voice referral procedures to obtain a referral code for all of the transactions that they process (since a [Get Merchant Information](/apis/payments-platform-rest/openapi/merchants/merchantsmerchant) request won’t work offline). For added security, the UTG will hold the tokenized CHD in an encrypted file until connectivity is reestablished.

Shift4’ Secure Offline Stand-In® (SOS) feature provides advanced offline processing by allowing a merchant to set a threshold (a maximum dollar value) below which they are comfortable issuing automatic “stand-in” authorizations without requesting voice authorizations. All transactions above this amount will prompt for voice authorization.

Warning
Not all transactions processed using SOS may be approved once the UTG comes back online. Also, transactions processed using SOS will not qualify as EMV transactions in a card-present environment. However, the benefits of being able to accept transactions while offline may be worth the risk for some merchant environments.

An interface can determine that the UTG was offline for a transaction by checking the `transaction.authSource` field in the response. A value of "O" indicates an offline transaction, while a value of "E" indicates an online transaction.  Once the merchant’s internet connectivity is restored, the UTG will transmit the transaction data and acquire authorizations (when required), and normal processing can continue.

During the certification process, you may be asked to run a few tests to make sure offline processing is working as expected. For additional information, see the [Configuring Offline Mode](https://s4-myportal.s3.amazonaws.com/downloads/documentation/utg/utg%20installation%20and%20configuration%20guide.pdf) section in the UTG Installation and Configuration Guide. Your API analyst will assist you with testing offline functionality when you’re ready to do so.

Starting with UTG version 3130, all new releases will have the Offline Mode feature enabled by default (offering a seamless transition between offline and online processing). As a result, Shift4 has removed the option to disable Offline Mode from UTG TuneUp. Instead, there are two options available to bypass this feature and they are described in the [Bypassing UTG Offline Mode](https://s4-myportal.s3.amazonaws.com/downloads/documentation/utg/bypassing%20utg%20offline%20mode.pdf) document.