Error: dynamodb atomic counter not working

A DynamoDB counter should be updated in one UpdateItem request. Reading a value, incrementing it locally and writing it back loses updates when callers run concurrently.

• Use ADD #count :one, with :one as a Number. A missing counter starts at zero.
• Alias the attribute name, for example { "#count": "count" }, because expression names can be reserved.
• Supply the full primary key and request ReturnValues: "UPDATED_NEW" to receive the updated counter.
• Do not mix native document-client values with low-level DynamoDB JSON descriptors.

An increment is atomic but not idempotent: a retry after an ambiguous timeout can increment twice. Use idempotency records or conditional transactions when a business event must count exactly once.

The SDK v3 counter example shows a complete request. See also AWS item operations.