Union qry is not needed here.
Qry :
SELECT COUNT (
IIf(invoiceType = "A' , 1, 0 ) ) AS [Count Of Invoice Type A],
COUNT ( IIf(invoiceType = "B' , 1, 0 ) ) AS [Count Of Invoice Type B]
FROM MYTABLE
[WHERE 'any Where condition here'] ;
Let me know if it does not work.
Alternatively you can...