I've been trying to install add-ons but it always gives the same error

[Of_Epish]

For the past 2 days I've been trying to install plug-ins to my server with no success and the problem isn't the server version or type but when I press on the Add-ons section It internal server error then when I scroll down the Add-ons installer there no Add-ons to be seen I can't even search then I refresh the page and sometimes it says internal server error but the default Add-ons are the this time and it allows me to search, so I search for the plug-in i want and I find it but then when I press on install it just says An Unknown Error Occurred please help. I'm trying to get my server up

[DuckyProgrammer]

Don't use the Addons page, download plugins from places like SpigotMC - High Performance Minecraft and upload them to File Manager -> Plugins.