Microsoft has phased out the generic 120-day trial key for Exchange 2019. For permanent installations, you must use a genuine VL key or contact your Microsoft licensing partner.
Run the following command in as Administrator: exchange 2019 product key invalid
Set-ExchangeServer -Identity "SERVERNAME" -ProductKey "XXXXX-XXXXX-XXXXX-XXXXX-XXXXX" Then restart the Exchange services or reboot. Microsoft has phased out the generic 120-day trial
Fix: "Product Key Invalid" Error When Installing Exchange Server 2019 exchange 2019 product key invalid
If using Exchange 2019 RTM or CU1–CU11, download the latest Cumulative Update 14 (CU14) or newer from the Microsoft Download Center. Newer CUs have better key handling.