My Minecraft server won't let others connect to it?

I just created a minecraft server for 1.8.9 so my friends and I can go on it, and although it'll let me connect and I can go on myself, my friends can't. They see my sever as "no connection" when it's really connected. Is there anything I'm doing wrong or something I need to fix? Thank you for anyone who helps it'll be greatly appreciated!

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