My 2020 return

I completed our joint return. My NY state return has a form included IT-588 which I don't understand why it is there, When completed my instructions were to mail the return and not efile, not sure why? I also don't know why it says I have a payment due then says I don't have any refund or amount due? I'm afraid I mad an error completing the return and don't know what to do and so far not finding anything helpful on your website.