If you are referring to the license activation code for TurboTax Desktop (Download Version) there's a few reasons why your code may not be working:
It can be because one digit (or more) is incorrect or you are trying to enter a code for TurboTax Online in a Desktop software (or vice-versa). The codes for TurboTax Online will not work with TurboTax Desktop and vice versa.
To find the correct License Code see the link below
How do I find my license code for TurboTax Desktop?
Make sure that you have properly installed the software and make any manual updates as needed
Other helpful links:
How do I get started with TurboTax Desktop?
Manually update TurboTax for Windows Software
