You wonder why the exception/error is not appearing though all the criteria you have set is matched.
SAP Business ByDesign
Default criteria : Same Supplier, External ID matched 80% or above and Invoice date + or - 7 days.
Additional criteria :what you set in BC activity "Supplier invoice exception "
In general ,
System will check and need all Default criteria to match between both invoices to raise exception
When all or one of the elements in default criteria does not match then only system will check for additional criteria other wise it will not check for them.
System will check and need all additional criteria to match between both invoices to raise exception
system will check for one more criteria that is PO reference only when additional criteria is used by system.
if both POs are same then error is raised
So in your case one of the default criteria
or one of additional criteria is not matched
or PO reference is not there in one of the invoice
or PO reference is not matched
Thus no error is appearing.
possible Duplicate, no exception , KBA , exception , SRD-SRM-SI , Supplier Invoicing , Problem