This is same problem I had for 2024 TurboTax. Activated on a PC, then downloaded on Mac and tried to activate it there. Said activation code had already been used. Was told at "Help" desk that I had to configure my Mac for PC using virtualization or Bootcamp in order for it to accept the activation code. Seems a bit crazy to have to do that! Continue to get messages from TurboTax that it can be done simply by downloading it on the 2nd operating system and using activation code. I logged into the same account used to buy the version put on the PC. It does not work. I had to buy another copy of the software!
