I have an LG27UD68-P freesync enabled Monitor and was having a ton of trouble enabling freesync. I was using an RX Vega 56 and an HDMI cord. Freesync didn't work until I went out and bought a display port cord. I know freesync says it works with HDMI and DP but you're likely better off getting a DP. Previously my monitor greyed out freesync until I switched, just thought I would help.
