For running J!5.1 you must https://fabrikar.com/forums/index.php?wiki/update-from-github/ or include the new file manually https://fabrikar.com/forums/index.php?threads/joomla-5-1-and-fabrik-cannot-find-files-error.54473/post-285151 See also Announcements
Please see our announcement here.
WHERE
Field: id
Condition: IN
Value: SELECT bills.id FROM bills LEFT JOIN customers ON customers.id = bills.customer WHERE customer.userid = '{$my->id}'
Type: Query
Apply to: customers