AI-generated Key Takeaways
- 
          CustomFieldValueError.Reason is an enumeration detailing the reasons for a target error related to custom fields. 
- 
          Possible reasons include a custom field or option not being found, a custom field being inactive, or an invalid entity type being used. 
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          The UNKNOWN reason is returned when the actual value is not exposed by the requested API version. 
The reasons for the target error.
- Namespace
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               https://www.google.com/apis/ads/publisher/v202508
| Enumeration | Description | 
|---|---|
| CUSTOM_FIELD_NOT_FOUND | An attempt was made to modify or create a CustomFieldValue for a CustomField that does not exist. | 
| CUSTOM_FIELD_INACTIVE | An attempt was made to create a new value for a custom field that is inactive. | 
| CUSTOM_FIELD_OPTION_NOT_FOUND | An attempt was made to modify or create a CustomFieldValue corresponding to a CustomFieldOption that could not be found. | 
| INVALID_ENTITY_TYPE | An attempt was made to modify or create a CustomFieldValue with an association to an entity of the wrong type for its field. | 
| UNKNOWN | The value returned if the actual value is not exposed by the requested API version. |