Hello
Here are some steps you can try:
Check the product key: Make sure the product key is correct and matches the edition of Windows Server you’re trying to activate. Sometimes, the product key for the retail version might not work with the evaluation version.
Use Command Prompt: You can try to activate Windows Server using Command Prompt. Here’s how:
Open Command Prompt as an administrator.
Enter the command slmgr.vbs /upk and press Enter. This will remove any old or trial keys.
Now enter the command slmgr.vbs /cpky.
Now use the command slmgr.vbs /ipk <your-product-key> to enter your new product key.
Finally, type slmgr.vbs /ato and press Enter to activate your Windows Server 2019.
Reinstall Windows Server: If the above steps don’t work, you might need to reinstall Windows Server with a non-evaluation ISO. Please make sure to back up any important data before doing this.