Little help understanding Tax Demand reason

Just been sent a tax demand for the 2022/23 and have been informed I underpaid by over £500 which is due by the end of Jan 24 . I have looked and the figures they have sent me and i have been allocated the standard 1257l tax code for my payments over that year . I have gone on line to try to understand this as I have just retired from my employer and my last payment from them was march 23 .. Included in my last wage was a bonus and as such took me into the higher tax bracket which is what it is but now i receive a demand and when i've check on line all the excuse is 'Given too much marriage allowance' but i cant seem to be able to find any other explanation ... I did claim an allowance from my wifes allowance whilst employed as she is on a very low income (less than 5k per annum) but this allowance had not been applied to 22/23 ... Have tried ringing to try to get some sort of understanding but kept getting 'very busy ' then getting cut off .

Hi kintekke,
If Marriage Allowance was in place, it would be removed if you went into the higher rate threshold.
If this was previously in your tax code for the year it would cause an underpayment.
Thank you.