Did you make a non-deductible contribution in 2024 or have a basis/balance in your IRA from prior years on Form 8606?
You need to go thru the steps in the Deductions & Credits / Traditional and Roth IRA Contributions to make sure you have the right starting basis in the IRA and record the contribution that was used for the Roth conversion.
On the 1099-R input there is an important question about "What did you do with the money" where you need to say it was moved to another retirement account, then "I did a combination or rolling over, converting..." then specify how much was converted to Roth.
This help page has all the steps, make sure to go through both sections and if still having issues it would be good to understand what is on your 8606 to see where the issue is.
https://ttlc.intuit.com/turbotax-support/en-us/help-article/retirement-benefits/enter-backdoor-roth-...
