My client still insists that he has already paid taxes on the distribution. He insists that I need to go back and amend the 2020 return taxes paid on the distribution and distribute the taxes paid on the distribution and the distribution over 3 years! He says that the IRS website agrees with his understanding as to how this should be done.  My way he says that he is paying taxes on the distribution twice! He has talked to several CPA's and they agree with him.

What can I do to convince him that taxes paid in a year are deducted in that year?