Error: DynamoDB ConditionalCheckFailedException

ConditionalCheckFailedException means the condition attached to a write evaluated to false. DynamoDB did not apply that write. This is often the intended protection against an overwrite or stale version.

1. Check the complete primary key: both partition and sort key when the table has both.
2. Compare the expected value and its type with the current item. A String and a Number are different types.
3. For a create-only put using attribute_not_exists(pk), an item already exists at that full key.
4. For optimistic locking, reload the current version and decide whether the update should still happen. Do not remove the condition just to make the error disappear.

Where supported, set ReturnValuesOnConditionCheckFailure: "ALL_OLD" to inspect the item associated with the failure. Treat that data as sensitive application data when logging.

See conditional writes, create-only examples and AWS error handling.