diff --git a/DOCUMENTATION.md b/DOCUMENTATION.md
index fe2ee97..bbc592e 100644
--- a/DOCUMENTATION.md
+++ b/DOCUMENTATION.md
@@ -2244,7 +2244,7 @@ Remove a device environment variable.
 ### Function: set(uuid_or_id, env_var_name, value) ⇒ <code>None</code>
 
 Set the value of a device config variable.
-
+Note that config variables must start with BALENA_ and RESIN_ prefixes.
 #### Args:
     uuid_or_id (Union[str, int]): device uuid (string) or id (int)
     env_var_name (str): environment variable name.
@@ -2252,7 +2252,7 @@ Set the value of a device config variable.
 
 #### Examples:
 ```python
->>> balena.models.device.config_var.device.set('8deb12','test_env4', 'testing1')
+>>> balena.models.device.config_var.set('8deb12','BALENA_test_env4', 'testing1')
 ```
 ## DeviceEnvVariable
 
diff --git a/balena/exceptions.py b/balena/exceptions.py
index c389b7f..cf57016 100644
--- a/balena/exceptions.py
+++ b/balena/exceptions.py
@@ -185,7 +185,7 @@ def __init__(self, body, status_code=None):
         self.message = Message.REQUEST_ERROR.format(body=body)
         self.body = body
         self.status_code = status_code
-        # print(self.message, status_code)
+        print(self.message, status_code)
 
 
 class NotLoggedIn(BalenaException):
diff --git a/balena/models/device.py b/balena/models/device.py
index 2c58ea6..d94ceb7 100644
--- a/balena/models/device.py
+++ b/balena/models/device.py
@@ -2145,14 +2145,14 @@ def get(self, uuid_or_id: Union[str, int], env_var_name: str) -> Optional[str]:
     def set(self, uuid_or_id: Union[str, int], env_var_name: str, value: str) -> None:
         """
         Set the value of a device config variable.
-
+        Note that config variables must start with BALENA_ and RESIN_ prefixes.
         Args:
             uuid_or_id (Union[str, int]): device uuid (string) or id (int)
             env_var_name (str): environment variable name.
             value (str): environment variable value.
 
         Examples:
-            >>> balena.models.device.config_var.device.set('8deb12','test_env4', 'testing1')
+            >>> balena.models.device.config_var.set('8deb12','BALENA_test_env4', 'testing1')
         """
         super(DeviceConfigVariable, self)._set(uuid_or_id, env_var_name, value)