To count daily transactions in Shopify (not how many items per customer), use timestamp.
SELECT
d.dt AS date,
COALESCE(COUNT(s.Paid_at),0) AS count
FROM (
SELECT DATE('2025-12-01') + INTERVAL n DAY AS dt
FROM (
SELECT 0 n UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4
UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9
UNION ALL SELECT 10 UNION ALL SELECT 11 UNION ALL SELECT 12 UNION ALL SELECT 13 UNION ALL SELECT 14
UNION ALL SELECT 15 UNION ALL SELECT 16 UNION ALL SELECT 17 UNION ALL SELECT 18 UNION ALL SELECT 19
UNION ALL SELECT 20 UNION ALL SELECT 21 UNION ALL SELECT 22 UNION ALL SELECT 23 UNION ALL SELECT 24
UNION ALL SELECT 25 UNION ALL SELECT 26 UNION ALL SELECT 27 UNION ALL SELECT 28 UNION ALL SELECT 29
UNION ALL SELECT 30
) nums
) d
LEFT JOIN shopify s
ON s.Paid_at IS NOT NULL
AND s.Paid_at <> ''
AND LEFT(s.Paid_at,10) = DATE_FORMAT(d.dt,'%Y-%m-%d')
GROUP BY d.dt
ORDER BY d.dt;