I have an amount in Box 12c for HSA contributions. When I enter it in TurboTax, it won't save. I've tried twice.

[h2orat01]

It also won't let me enter this amount in the HSA in deductions

[LeticiaF1]

If what you are referring to is an issue when entering your Box 12 amount in your W2.  You can try getting out of your program and going back in, clearing your cache and cookies, or trying a different Web Browser.
 

If this does not resolve your issue, then delete your W2 and enter it again.  Once you are able to enter your information for your W2 the entries for your HSA will be easier.  Make sure you do not enter your contributions again.  

Here’s how to go back and review your HSA entries in TurboTax:

1. Open (continue) your return in TurboTax
2. In the search bar, search for HSA and select the Jump to link in the search results
3. On the screen Tell us about the health-related accounts you had in 2023, check the box next to Health Savings Account (HSA) and select Continue
4. If you land on Your HSA summary, select Edit, then make sure the Health Savings Account (HSA) box is checked on the next screen and select Continue. If you see the screen Here’s what we have so far, select Done
5. Answer No to Did you inherit this HSA?
6. Do not enter your contribution on the screen Let’s enter your HSA contributions and select Continue
7. Continue answering the questions until you reach Your HSA summary

How do I delete a tax form in TurboTax Desktop?

[Opus 17]

Lines 12a, 12b, 12c and 12d are not really separate lines on your W-2.  They are all "box 12" items.  Some employers use a, b, c and d when they need to list multiple things, but the order or lower case letter is not important, what matters is the capital letter code.  Select the code (W for HSA) and enter the amount.  Don't try to combine the letter c and code W, and don't use "c" as the code.