How would you rewrite this query to be MySQL 5.7 friendly? Currently fails due to new GROUP BY rules.

wtf.sql

select extf.* from (
	select ExternalTransactinId 
	from ebay_order_items
	ExternalTransactionId is not null
	group by ExternalTransactionID
) extf
extf.z_shipmentno is null 
and extf.orderstatus = 'Completed' 
and extf.timestamp > '2015-02-25' 
order by extf.timestamp desc;