When you spawn one of a few modbots, you can't press E on it to get the mod. This happen due to people already have all weapon mods by default. All what you need to do is following the tutorial down here to solve the problem.

Open the spawnmenu -> go to Utilities tab -> Find "Admin Weapon Options" on DOOM category and tick the "Enable weapon mods?" box + disable "Players have all weapon mods?"

With this setting, all weapon mods are still enable to be used, but you will have to get them manually through modbot.