As of Minecraft 1.13, Mojang have changed the location where the Minecraft server is to be downloaded from. This means that both McMyAdmin 2 and AMP need updating to accommodate this.
AMP users simply need to update to the latest version of AMP.
McMyAdmin 2 users with a Pro licence should consider upgrading to AMP, but if that's not possible you will need to obtain the server manually, rename the server to
minecraft_server.jar and upload it.
In McMyAdmin 2 sleep mode is also not available at this time for 1.13+, but it does function correctly in AMP.