Using the Plaid /transactions/sync API endpoint is a good approach to retrieve all historical transaction data for an account. When you use the API with cursor set as an empty string (""), you are effectively starting from the beginning of the transaction history. Plaid will return the initial batch of transactions and provide a next_cursor value, which you should use in subsequent requests to get the next batch of transactions. This process should be repeated until next_cursor is null, indicating there are no more transactions to fetch.

To handle synchronization effectively, you should process the batches in the order they are received, and always use the next_cursor from the current response to fetch the next batch. This way, you maintain the integrity and sequence of the transaction data according to how Plaid provides it.

Remember to handle edge cases, like re-synchronization if a batch fails or if there is a long delay between fetches, to ensure your local copy of the transactions remains accurate and up-to-date.