I restarted the server and it worked. Thanks for your help 
Posts by Arjunbrunei
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What software is installed on your server? Do you have any plugins?
Are you OP on your server?
I've already fixed it. now it works but now my friends cannot join the server, java.io exception
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Guys, I just started playing on my server and for some reason I can't destroy or place any blocks. I am on creative mode and using minecraft 1.13.2. Please help