BigQuery Window functions

I want to calculate a 10 day rolling sum. The problem is that the time is not regular, eg sometimes we have a couple of observation on the same date and then some dates are missing in between.

Mock data looks as following:

My idea was to use a window function, together with sum(if(date_diff_10_days <= order_completed_at , order_amount,0 ))

select 
* ,
sum(if(
  date_diff_10_days <= order_completed_at 
  , order_amount, 0)) as sum_10_days
  OVER (PARTITION BY customer_id order by order_completed_at asc
  ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW) 
from mock_data

The query returns a cumulative sum over all records and not only of records within a 10 days time window. Does somebody have idea how I can fix my query?

I created a sample query order_id, order_completed_at , order_amount and calculated the rolling sum for last 10 days.I dont have Big Query, so unable to test. I have used postgres as an example.

Fiddle

I have used additional dates to test scenarios in the fiddle, let me know

WITH rolling_sum AS (
    SELECT 
        o1.order_id,
        o1.order_completed_at,
        o1.order_amount,
        o1.customer_id,
        SUM(o2.order_amount) AS sum_10_days
    FROM orders o1
    JOIN orders o2
        ON o1.customer_id = o2.customer_id
        AND o2.order_completed_at >= o1.order_completed_at - INTERVAL '10 days'
        AND o2.order_completed_at <= o1.order_completed_at
    GROUP BY 
        o1.order_id,
        o1.order_completed_at,
        o1.order_amount,
        o1.customer_id
)
SELECT * FROM rolling_sum
  ORDER BY order_id;

Output