How to dynamically select purchases based on a date slicer where the purchase is the first per user

Hi RogerSteinberg Please try below. You were missing ALL.

testing_testing = 
var min_date =
    CALCULATE(
        MIN(test[date]),
        ALLSELECTED(test[date])
    )

var customers =
    values(test[user_id])

var priorcustomers = 
    CALCULATETABLE(
        VALUES(test[user_id]),
        FILTER(
        all(test),
            test[date] < min_date
        )
    )
    
return
COUNTROWS(
    EXCEPT(
        customers,
        priorcustomers
    )
)

Thanks
Ankit Jain
Do Mark it as solution if the response resolved your problem. Do Kudo the response if it seems good and helpful.