diff --git a/README.md b/README.md
index 8a2c5c82e..822e2acd2 100644
--- a/README.md
+++ b/README.md
@@ -560,7 +560,21 @@ allow_oauth2_login=true
 oauth2.jwk_set.url=https://www.googleapis.com/oauth2/v3/certs
 ```
 ---
-   
+
+## Frozen APIs
+API versions may be marked as "STABLE", if changes are made to an API which has been marked as "STABLE", then unit test `FrozenClassTest`  will fail.
+### Changes to "STABLE" api cause the tests fail: 
+* modify request or response body structure of apis
+* add or delete apis
+* change the apis versionStatus from or to "STABLE"
+
+If is is required for a "STABLE" api to be changed, then the class metadata must be regenerated using the FrozenClassUtil (see how to freeze an api)
+### Steps to freeze an api
+* Run the FrozenClassUtil to regenerate persist file of frozen apis information, the file is `PROJECT_ROOT_PATH/obp-api/src/test/resources/frozen_type_meta_data`
+* push the file `frozen_type_meta_data` to github
+
+There is a video about the detail: [demonstrate the detail of the feature](https://www.youtube.com/watch?v=m9iYCSM0bKA)
+
 ## Scala / Lift
 
 * We use scala and liftweb http://www.liftweb.net/
diff --git a/obp-api/src/test/scala/code/util/FrozenClassTest.scala b/obp-api/src/test/scala/code/util/FrozenClassTest.scala
index 8161fa690..8951e392b 100644
--- a/obp-api/src/test/scala/code/util/FrozenClassTest.scala
+++ b/obp-api/src/test/scala/code/util/FrozenClassTest.scala
@@ -64,13 +64,13 @@ class FrozenClassTest extends ServerSetup {
             (typeName, fields) <- typeNameToTypeValFields.toList
             if(pTypeName == typeName && pFields != fields)
           } yield {
-            val expectStructure = pFields.map(pair => s"${pair._1}:${pair._2}").mkString("(", ", ", ")")
+            val expectedStructure = pFields.map(pair => s"${pair._1}:${pair._2}").mkString("(", ", ", ")")
             val actualStructure = fields.map(pair => s"${pair._1}:${pair._2}").mkString("(", ", ", ")")
 
             s"""
                |{
                | typeName: $typeName
-               | expectStructure: $expectStructure
+               | expectedStructure: $expectedStructure
                | actualStructure: $actualStructure
                |}
                |""".stripMargin