Hi @traut,
I had to remove your screenshot because it included your license key for Stacks. That shouldn’t be made public.
We don’t sell Stacks, that is sold by Yourhead Software which is a third-party developer. They are listed on our Marketplace along with a lot of other third-party developers’ products. Unfortunately we can’t help with licensing issues for third-party products as we do not have any kind of access to their licensing system.
If your Stacks license key is not working, you will need to reach out to YourHead software directly. We have their contact information listed here I need help with Stacks, what should I do?
If you don’t hear back from them in a timely manner please let us know and we will try to help escalate your case with them.
One thing to try though, make sure you are downloading the correct version of Stacks that your license key is valid for. It looks like you are trying to enter you license key in Stacks version 5. Perhaps your license key is for an earlier version, like version 4 or version 3. You can download earlier versions of Stacks from their archive page here Stacks. Give that a try and see if it helps.