Date comparison is not happening in op:eq function in optical query

Question

I am trying to compare the dates in optical query but its not working as expected. Below is my optical query

let $lastDay := '2021-01-31'
op:as("BalanceAmount", op:case((
        op:when(op:eq(op:view-col("Table1", "InvoiceDate"), $lastDay), ("Table1", "BalanceAmount"))),
        op:view-col("Table1", "InitialAmount")))

above query is not working as expected and when the InvoiceDate matches to $lastDay value, I am not getting correct value