If Pro Email is a confirmation field (checkbox) then setting the query’s field_value parameter to true will work.
SInce all you are wanting to do is check that the field has been set, I think this version of the query will work better for you. It removes the field_value parameter and checks that the named field has been set with (ucf.value = '') IS NOT TRUE. This will return false for any users who have not set the field, and will also return false for users who have set the field and then deleted the value they set:
--[params]
-- string :field_name
-- string :group_name
WITH ucf_name AS(
SELECT
CONCAT('user_field_', id) AS name
FROM user_fields
WHERE name = :field_name
),
excluded_users AS (
SELECT
gu.user_id
FROM group_users gu
JOIN groups g
ON g.id = gu.group_id
WHERE g.name = :group_name
)
SELECT
u.id AS user_id
FROM users u
JOIN user_custom_fields ucf
ON ucf.user_id = u.id
WHERE ucf.name = (SELECT name FROM ucf_name)
AND (ucf.value = '') IS NOT TRUE
AND u.id NOT IN (SELECT user_id FROM excluded_users)
If you’d like the query to return the field’s value, change the final select statement to:
SELECT
u.id AS user_id,
ucf.value
FROM users u
JOIN user_custom_fields ucf
ON ucf.user_id = u.id
WHERE ucf.name = (SELECT name FROM ucf_name)
AND (ucf.value = '') IS NOT TRUE
AND u.id NOT IN (SELECT user_id FROM excluded_users)