AI-generated Key Takeaways
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          This enum describes possible errors related to feed items. 
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          Errors include issues with invalid or unknown fields and types. 
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          Mismatches and multiple mappings are common causes of errors. 
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          Some errors relate to operations on specific feed types like system-generated or typed feeds. 
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          Missing fields and read-only feeds can also cause errors. 
Enum describing possible feed item errors.
| Enums | |
|---|---|
| 
 | Enum unspecified. | 
| 
 | The received error code is not known in this version. | 
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 | The given placeholder field does not exist. | 
| 
 | The given criterion field does not exist. | 
| 
 | The given placeholder type does not exist. | 
| 
 | The given criterion type does not exist. | 
| 
 | A feed mapping must contain at least one attribute field mapping. | 
| 
 | The type of the feed attribute referenced in the attribute field mapping must match the type of the placeholder field. | 
| 
 | A feed mapping for a system generated feed cannot be operated on. | 
| 
 | Only one feed mapping for a placeholder type is allowed per feed or customer (depending on the placeholder type). | 
| 
 | Only one feed mapping for a criterion type is allowed per customer. | 
| 
 | Only one feed attribute mapping for a placeholder field is allowed (depending on the placeholder type). | 
| 
 | Only one feed attribute mapping for a criterion field is allowed (depending on the criterion type). | 
| 
 | This feed mapping may not contain any explicit attribute field mappings. | 
| 
 | Location placeholder feed mappings can only be created for Places feeds. | 
| 
 | Mappings for typed feeds cannot be modified. | 
| 
 | The given placeholder type can only be mapped to system generated feeds. | 
| 
 | The given placeholder type cannot be mapped to a system generated feed with the given type. | 
| 
 | The "field" oneof was not set in an AttributeFieldMapping. | 
| 
 | Feed is read only. |