Invoice Checking for automation purposes

Hi PBI Community

I want to create a DAX measure which returns a

"✓" when the invoice amount posted is equal to the same as the previous journal entry posting.
and a
"✗" when the invoice amount is different.

It needs to be conditional on the Amount being posted to the same G/L Account ID and the same Vendor Name.

I made the following, but it doesn't consider the element of previous journal entry posting or whether it is the first posting for that Vendor and related G/L Account ID.

Automation Check = 
if(ISBLANK([TY (EUR)]),
blank(),
IF(CALCULATE([TY (EUR)] / [€ Avg.]) = [# Postings],
   FORMAT("✓", "Green"),
   FORMAT("✗", "#Red")
))

How could I change it so that the measure returns "x" when it is first postings as well, and not only compares total amount / avg. posting = count of postings.

The matrix visualization looks like this right now: