Problems installing RDS CALs on a 2019 license server

Good morning.  I had an interesting issue this morning I figured I would share.  I had a customer that was having a tough time installing his RDS CALs.  At both and in the install license wizard we were receiving the error “Invalid license code” and “The serial number is not valid.” respectively.  I assumed this was due to a bad license code, as I have seen that a couple of times in the past.  After emailing Microsoft, I was able to confirm the license code was good. 

The serial number is not valid.

After going back to my customer, I found out that the license server was running Windows 2019.  Normally this should not be a problem as you can install down-level CALs.  For instance, it is possible to install 2012 RDS CALs on a 2016 license server.  It appears that may no longer be the case with 2019 or this may be a bug.  Time will tell.  In the end we fixed the problem by installing licensing on the Windows 2016 server.  The CALs then installed without issue.

If this changes in the future I will update this blog post.  I hope you found this blog post useful.  If you have any corrections or anything to add, please do so in the comments below.