This page provides a download link for the Minecraft server jar, but the link is invalid. The link directs the user to download 1.14.3-Pre-Release-4, not the official release for 1.14.3. Using the jar provided in the link rejects attempts to connect when a client is using 1.14.3 and not the pre-release-4.
As of 5 Mins ago this issue was NOT resolved.
The correct link is this one:
https://launcher.mojang.com/v1/objects/d0d0fe2b1dc6ab4c65554cb734270872b72dadd6/server.jar
The one given on the 1.14.3 patch notes page is incorrect. The one given on the server hosting page is correct.