Value provided in ExpressionAttributeNames unused in expressions

TL;DR — You declared a name placeholder in ExpressionAttributeNames (e.g. #status) that no expression references. DynamoDB requires every declared alias to be used in a KeyConditionExpression, FilterExpression, UpdateExpression, ConditionExpression, or ProjectionExpression. Remove the unused alias — or fix the expression that was supposed to reference it.

What it means

ValidationException: Value provided in ExpressionAttributeNames unused in
expressions: keys: {#status}

ExpressionAttributeNames is a substitution map for attribute-name aliases (needed for reserved words or names with special characters). DynamoDB enforces a strict two-way contract: every alias you use in an expression must be declared, and every alias you declare must be used. A leftover, unreferenced entry triggers this HTTP 400 ValidationException. It's client-side and not retryable until the map matches the expressions.

Why it happens

• A stale alias left after editing an expression — you removed #status = :s from the expression but forgot to delete #status from the names map.
• A generated map that over-declares — a mapping layer emitted aliases for every attribute even ones the final expression doesn't touch.
• The alias is in the values map, not names — you meant :status (a value) but declared #status (a name).
• A typo mismatch — the expression uses #stat while the map declares #status, so #status is technically unused.

How to fix it

1. Delete the unused alias the message names from ExpressionAttributeNames.
2. Keep the map in lock-step with the expressions — declare a #name only when an expression actually references it.
3. Check for a name-vs-value mix-up — #-aliases live in ExpressionAttributeNames, :-placeholders in ExpressionAttributeValues.
4. Regenerate the request so names, values, and expression text are built together rather than assembled by hand.

Related errors

• Value provided in ExpressionAttributeValues unused in expressions — the same rule for :value placeholders.
• An expression attribute name used in the document path is not defined — the reverse: a used alias that was never declared.
• Attribute name is a reserved keyword — why you needed a #-alias in the first place.