TT is lowering my refund when I enter the 1095-A

When the 1095-A from Market Place insurance was entered, TT is claiming that the credit the market place gave is too high and is wanting my son to pay over $500 more for his insurance.  It said he made more money than he had estimated.  He made exactly the amount he reported to Market Place who gave him the credit.  Market Place did give extra credit based on the amount he contributed every month to a Roth IRA. Why is TT thinking he got too much credit?  How can we double check TT's calculations?  Maybe TT is not aware of the additional credit MP offered him for putting $300 a month into a Roth IRA?