dbt incremental model ap kreye duplicate records

Mwen gen yon dbt incremental model ki ap chaje done chak jou nan Snowflake. Men apre plizyè jou, mwen remake menm records yo parèt plizyè fwa nan destination table la.

What I tried

Mwen mete unique_key='transaction_id', men duplicate yo toujou ap parèt.
 
{{ config(
    materialized='incremental',
    unique_key='transaction_id'
) }}
 
SELECT
    transaction_id,
    customer_id,
    amount,
    transaction_date
FROM {{ source('sales', 'transactions') }}
 
{% if is_incremental() %}
WHERE transaction_date >= (
    SELECT MAX(transaction_date)
    FROM {{ this }}
)
{% endif %}

Error message

transaction_id | count
---------------|------
10001          | 3
10002          | 2
10003          | 4

Expected result

Chak transaction_id ta dwe parèt sèlman yon sèl fwa nan final table la.