IReport “parameter Not Found” when adding a parameter

i'm using IReport 4.8.0. i created a dataset and using it for a table and a chart and everything works fine.

now i want to add a string parameter so the user can insert a name of city.

so i added a new string parameter inside the dataset and dragged it into Page Header. i also updated the Dataset query so it will receive the value from the parameter:

SELECT
 COUNT(leads.`status`) AS Number_Of_Status,
 leads.`status` AS leads_status,
 leads.`primary_address_city` AS leads_primary_address_city
FROM
 `leads` leads
WHERE
 leads.`primary_address_city` = $P{city_to_choose}
GROUP BY
 leads.`status`

but all i get when pushing the "preview" is "Parameter Not Found: city_to_choose" what did i miss?