Interface Limitation (EAC vs. PowerShell): The graphical Exchange Admin Center (EAC) frequently returns "invalid" errors even when a key is perfectly valid.
Replace EXCH01 with your server name and the key with your actual key (hyphens optional). exchange 2019 product key invalid
Set-ExchangeServer -Identity
Here is a guide on troubleshooting this issue, followed by a special "PowerShell Utility" feature script designed to help you diagnose the problem quickly. Standard Edition – For small to medium organizations
Since Exchange Server 2019 is a complex enterprise product, there are several reasons why a key might be rejected, ranging from simple typos to version mismatches.
Edition Mismatch: You may be trying to enter a Standard edition key on a server that needs to be Enterprise, or vice-versa. Note that while you can upgrade from Standard to Enterprise, you cannot downgrade without a full reinstallation.