In 1809 this SKU is called Windows 10 Enterprise for Virtual Desktops and its KMS SN is:
In 1803 this SKU is called Windows 10 Remote Server and its KMS SN is:
In fact the later SN which is listed in "Microsoft Toolkit 2.6.4" for "Windows Server 2016 Remote Server" applies to both 1809 and 1803. I have tried this myself.
To convert your Windows edition to ServerRDSH, f
irst you should install the KMS key of "Windows Server 2016 Remote Server".
Second you should active this Windows copy.
Both can be done in "Microsoft Toolkit 2.6.4" which is the last version. Anything later than 2.6.4 are fake.
In 1803 we should "dism /online /enable-feature /featurename:appserverclient" to enable RDSH role which in 1809 does not need to be added manually.
With RDSH role enabled there can be unlimited concurrent remote user logins.
We can have a look of if this role is enabled by using "Remote Desktop Licensing Diagnoser" tool from "WindowsTH-RSAT_WS_1803-x64.msu" in 1803 while in 1809 the tool is to be added through "optional features".
At last, there is a latent issue brought about by RDSH role. That is "The Remote Desktop Session Host server is within its grace period, but the RD Session Host server has not been configured with any license server." as is stated by the aforementioned tool. To solve this issue we should either buy licenses from Microsoft or use a script named "Reset-TSGracePeriod.ps1" ( which can be download from here:
https://gallery.technet.microsoft.com/scriptcenter/Reset-Terminal-Server-RDS-44922d91 ) to keep RDSH role functional indefinitely cause when the grace period is over not even a single RDP connection will be allowed and an administrator has to "dism /online /disable-feature /featurename:appserverclient" to restore the server's ability to accept 2 concurrent users logins as a normal feature of a Microsoft server OS without RDSH role.
The script will rest the grace period to 120 days by deleting a registry key that is "Computer\HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Terminal Server\RCM\GracePeriod".