Index & Match Formula for Unique Values On Multiple Criteria

Here is a low tech proposal.
Populate column R on the Master Invoice Entry sheet using: =IF(A2<>A1,1,"")
Populate the range D24:D31 on the desired results sheets using*:

Formula:

=IFERROR(INDEX('Master Invoice Entry'!A$2:A$31,SMALL(IF('Master Invoice Entry'!B$2:B$31=B$17,IF('Master Invoice Entry'!C$2:C$31=N$9,IF('Master Invoice Entry'!$R$2:$R$31=1,ROW($2:$31)))),ROW(1:1))),"")

*Denotes an array entered formula that needs to be confirmed by pressing CTRL+SHIFT+ENTER to activate the array, not just ENTER. You will know the array is active when you see curly braces { } appear around your formula. If you do not CTRL+SHIFT+ENTER you will get an error or a clearly incorrect answer.
Let us know if you have any questions.