i used Powershell then:

Dism /online /Set-Edition:ServerStandard /AcceptEula /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

replace xxxxx with your code purchased.

I was extremely worried that this would be some sort of scam but this legit worked to activate my windows server 2022 standard so that I can operate my Minecraft server and 7 days to die server while being legit.

Works as described, bought and activated via dism in 5 minutes. Can recommend!

I try also with Powershell, but get a error, change a little step and it works. I use CMD instead of Powershell, then type :

Dism /online /Set-Edition:ServerStandard /AcceptEula /ProductKey:XXXXX-XXXXX-XXXXX-XXXXX-XXXXX

It didn't work at first, as simple as it should, but after some search I found how to activate it from powershell and worked perfectly.
Launch a PowerShell as an Administrator
Type dism /online /get-currentedition and press ENTER
Type dism /online /get-targeteditions and press ENTER
Type dism /online /set-edition:serverstandard /productkey:<KEY-KEY-KEY-KEY-KEY> /accepteula and press ENTER