I am not sure which part you are stating is not correct. The intention is to contribute after-tax income. For your situation, a better move would be for you to

I am not sure which part you are stating is not correct. The intention is to contribute after-tax income. For your situation, a better move would be for you to do a Roth Conversion of the money in your traditional-IRA to move it to Roth IRA dollars. You do this with your broker, and then file form 8606 with the IRS. The $6,000 "Roth Backdoor" is indeed with post-tax dollars. This is intended. There are significant benefits to having the majority of your retirement savings in a Roth, including no minimum distributions, and the ability to withdraw funds for unqualified reasons 5 years after your last contribution. This is not financial advice, hire your own fiduciary financial advisor