You have a recordset on your clientStatus_contact.php plugin with:
SELECT username FROM users WHERE users.active = ?
But you are passing in the customers_id from the customers table. I don't see a way to filter that list from the customers_id since there doesn't seem to be a column in your users table that matches the customers_id. What column did you want to use as the filter? Are you sure it is based on the Client field?