I cannot join "Premium" type servers

Since can I bought a Minecraft version on the Minecraft.net site, I installed normally the laucher provided for this purpose and I wanted to play with my friends has Hypixel But they give me an error message "Failed to login: The authentication servers are currently down for maintenance "
As in the catch if against. I don't know why this error message is there because I paid for my games and would like to play them.
Can you help me because this problem is annoying,
Yours
Lucas