Thanks, that worked! Now I need to go back to basics and SETS:
SELECT
cost_details->'Accounting'->jsonb_object_keys(cost_details->'Accounting')->'BalanceUUID'
AS BalanceUUID,
cost_details->'Accounting'->jsonb_object_keys(cost_details->'Accounting')->'Units'
AS Cost
FROM cdrs
WHERE cost > 0
AND cost_details->'AccountSummary'->'BalanceSummaries' @>
'[{"ID":"B_MONETARY_POSTPAID"}]'
AND cost_details->'AccountSummary'->'BalanceSummaries' @>
json_build_object('UUID',
cost_details->'Accounting'->jsonb_object_keys(cost_details->'Accounting')->'BalanceUUID')::jsonb
limit 1;
ERROR: argument of AND must not return a set
LINE 1: ...ummaries' @> '[{"ID":"B_MONETARY_POSTPAID"}]' AND cost_detai...