/cmodify <name> in order to allow your friend access to your chest. It must be done with every chest you place. And use /permissiontrust <name> or /trust <name> to give them access to your plot overall.

I watched you mine for a while and watched you dig directly into diamond several times. You were on the server for 2 hours and had full diamond tools along with half a stack of diamond. All of this combined to me seemed like x-ray. I understand some players use sporadic mining techniques but yours c...

If you could provide a link for us to consider I will gladly look into it. Spigot would be the most reputable source!