Cannot overclock AMD GPU on Ubuntu 18.04 LTS

I am trying to overclock the memory on my GPU with AMDGPU Pro 18.40 driver. Nonetheless, /sys/class/drm/card0/device/pp_od_clk_voltage is an empty file and I cannot write to it. When I try echo "m 2 1600 950" > /sys/class/drm/card0/device/pp_od_clk_voltage as root it produces the following error: -bash: echo: write error: Invalid argument I have amdgpu.ppfeaturemask=0xffffffff in GRUB_CMDLINE_LINUX_DEFAULT in /etc/default/grub. I have also tried running: echo manual | sudo tee /sys/class/drm/card0/device/power_dpm_force_performance_level My question is based on the answer to the following question: https://unix.stackexchange.com/questions/404780/cant-overclock-gpu-using-amdgpu-driver-on-archlinux The author claims that this method works, however it obviously does not.