Hi and welcome to the forum

See if this is what you are after?
=SUMIFS(Data!$D$2:$D$20,Data!$A$2:$A$20,'FCST Counts'!A5,Data!$B$2:$B$20,'FCST Counts'!A2,Data!$C$2:$C$20,'FCST Counts'!A8)