Cannot play multiplayer

This has happened to a lot of people and the problem is when I try to play multiplayer or join realms it quotes, "Multiplayer is disabled. Please check your Microsoft account settings;" and I just don't know where to check and I checked all the places I could think of but I just can't enable it. If it was to do with making a Mojang account then I can't do that because you could only make an account in 2012. If I have to pay for multiplayer, please send me an email back with a link that takes me to the purchasing site and I did buy the full version of Minecraft Java.