diff --git a/common/models/subscription.js b/common/models/subscription.js
index 3d6f519..2687b02 100644
--- a/common/models/subscription.js
+++ b/common/models/subscription.js
@@ -773,19 +773,22 @@ module.exports = function (Subscription) {
       Reference: '5eb9e53ac8de837a99fd214a',
       OutgoingMessageID: '789091964',
       MessageNumber: '59255257',
-      hash: '1111' 
+      notifyBCSwiftKey: '1111' 
     }
     */
     let smsConfig = Subscription.app.get('sms')
-    if (smsConfig.swift && smsConfig.swift.notifyBCSwiftKey) {
-      if (
-        smsConfig.swift.notifyBCSwiftKey !==
-        options.httpContext.req.body.notifyBCSwiftKey
-      ) {
-        let error = new Error('Forbidden')
-        error.status = 403
-        throw error
-      }
+    if (!smsConfig || !smsConfig.swift || !smsConfig.swift.notifyBCSwiftKey) {
+      let error = new Error('Forbidden')
+      error.status = 403
+      throw error
+    }
+    if (
+      smsConfig.swift.notifyBCSwiftKey !==
+      options.httpContext.req.body.notifyBCSwiftKey
+    ) {
+      let error = new Error('Forbidden')
+      error.status = 403
+      throw error
     }
     let whereClause = {
       state: 'confirmed',
diff --git a/docs/_docs/config-sms.md b/docs/_docs/config-sms.md
index 7a34118..8355a9e 100644
--- a/docs/_docs/config-sms.md
+++ b/docs/_docs/config-sms.md
@@ -4,12 +4,12 @@ title: SMS
 permalink: /docs/config-sms/
 ---
 
-*NotifyBC* depends on underlying SMS service providers to deliver SMS messages. The supported service providers are
+_NotifyBC_ depends on underlying SMS service providers to deliver SMS messages. The supported service providers are
 
- * [Twilio](https://twilio.com/) (default)
- * [Swift](https://www.swiftsmsgateway.com)
+- [Twilio](https://twilio.com/) (default)
+- [Swift](https://www.swiftsmsgateway.com)
 
-Only one service provider can be chosen per installation. To change service provider, add following *smsServiceProvider* config object to file */server/config.local.js*
+Only one service provider can be chosen per installation. To change service provider, add following _smsServiceProvider_ config object to file _/server/config.local.js_
 
 ```js
 module.exports = {
@@ -17,10 +17,12 @@ module.exports = {
   smsServiceProvider: 'swift'
 }
 ```
+
 The rest configs are service provider specific. You should have an account with the chosen service provider before proceeding.
 
 ## Twilio
-Add *sms.twilio* config object to file */server/config.local.js*
+
+Add _sms.twilio_ config object to file _/server/config.local.js_
 
 ```js
 module.exports = {
@@ -28,24 +30,56 @@ module.exports = {
     twilio: {
       accountSid: '<AccountSid>',
       authToken: '<AuthToken>',
-      fromNumber: '<FromNumber>'
-    }
-  }
+      fromNumber: '<FromNumber>',
+    },
+  },
 }
 ```
-Obtain *\<AccountSid\>*, *\<AuthToken\>* and *\<FromNumber\>* from your Twilio account.
+
+Obtain _\<AccountSid\>_, _\<AuthToken\>_ and _\<FromNumber\>_ from your Twilio account.
 
 ## Swift
-Add *sms.swift* config object to file */server/config.local.js*
+
+Add _sms.swift_ config object to file _/server/config.local.js_
 
 ```js
 module.exports = {
   sms: {
     swift: {
-      accountKey: '<accountKey>'
-    }
-  }
+      accountKey: '<accountKey>',
+    },
+  },
 }
 ```
-Obtain *\<accountKey\>* from your Swift account.
 
+Obtain _\<accountKey\>_ from your Swift account.
+
+### Unsubscription by replying a keyword
+
+With Swift short code, sms user can unsubscribe by replying to a sms message with a keyword. The keyword must be pre-registered with Swift.
+
+To enable this feature, 
+
+1. Generate a random string, hereafter referred to as *\<randomly-genereated-string\>*
+2. Add it to _sms.swift.notifyBCSwiftKey_ in file _/server/config.local.js_
+
+   ```js
+    module.exports = {
+      sms: {
+        swift: {
+          ...
+          notifyBCSwiftKey: '<randomly-genereated-string>',
+        },
+      },
+    }
+   ```
+3. Go to Swift web admin console, click *Number Management* tab
+4. Click *Launch* button next to *Manage Short Code Keywords* 
+5. Click *Features* button next to the registered keyword(s). A keyword may have multiple entries. In such case do this for each entry.
+6. Click *Redirect To Webpage* tab in the popup window
+7. Enter following information in the tab
+   * set *URL* to *\<NotifyBCHttpHost\>/api/subscriptions/swift*, where *\<NotifyBCHttpHost\>* is NotifyBC HTTP host name and should be the same as [HTTP Host](../config-httpHost/) config
+   * set *Method* to *POST*
+   * set *Custom Parameter 1 Name* to *notifyBCSwiftKey*
+   * set *Custom Parameter 1 Value* to *\<randomly-genereated-string\>*
+8. Click *Save Changes* button and then *Done*
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