It's Enable Flying in Server Properties in the control panel.
It's a built-in anti-cheat that gets a little overzealous with certain mods, feather falling potions... standing on fences just right...
#"Flying is not enabled on this server"
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You need to restart the server for the change to apply.
For some things in Server Properties it only saves if the server is stopped while you change it, so rule of thumb is to stop, change, then start.
boreal ermine
Alright, I've got another for you. How do I give admin perms in the server, I was trying to set some things up but don't have the perms for it. And heads up it might be a while cause I'm starting work soon and won't be back for a good few hours.
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!minecraftop
quiet muskBOT
boreal ermine
Alright, I think I am getting the hang of it. Thank you for the assistance and time it was very helpful.