Maybe
=IFERROR(IF(OR(VLOOKUP(A2,'Stock Provision'!$A:$B,2,0)=SUMIF(A$2:A2,A2,D$2:D2),VLOOKUP(A2,'Stock Provision'!$A:$B,2,0)>SUMIF(A$2:A2,A2,D$2:D2)),D2,IF(VLOOKUP(A2,'Stock Provision'!$A:$B,2,0)<SUMIF(A$2:A2,A2,D$2:D2),VLOOKUP(A2,'Stock Provision'!$A:$B,2,0),0)),"")
Good luck!