SUMif with Vlookup or Match

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Can someone help me modify a sumif formula that requires a vlookup or a match.

Here is my sumif
-SUMIF('Tier 1'!R:R,">0",'Tier 1'!P:P)-SUMIF('Tier 2'!R:R,">0",'Tier 2'!P:P)
However before this sumif can function in need to have it match or lookup text to the left and match it before it sums.

SUMIF('FGs Inventory'!J:J,B31,'FGs Inventory'!AE:AE) In this example B31 is my match


IN other words in need to combine the following two Sumif into one

1. SUMIF('FGs Inventory'!J:J,B31,'FGs Inventory'!AE:AE)
2. -SUMIF('Tier 1'!R:R,">0",'Tier 1'!P:P)-SUMIF('Tier 2'!R:R,">0",'Tier 2'!P:P)