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First of all make sure you are using the correct IP:play.potterworldmc.com without any extra spaces, dots or anything (especially in the front). Then, try reloading your entire minecraft and check out the Technical Difficulties FAQ here.
I hope that works and if it does not, feel free to respond again below!
It is still not working for me. Says its outdated, what version of minecraft does this support? says "Outdated server! Im still on {0}" (Photo sent on server)
Our Server currently only supports 1.10 to 1.13, so you'll need to change your Minecraft version in order to join. If you're unable to figure out how to, please check out this website
Have you tried restarting your game? Also, are you using a paid-for version of Minecraft Java? Our server only supports official accounts and not cracked ones if this is the case.