How to best use Sliders in UE 4.26

Hello,
I’m trying to get sliders to set and keep data. The sliders are working at setting volume values, however when I come back to the audio screen, they are reset to 0 every time. I have got persistent variables in the Game Instance and Character BPs, but when I’m trying to set the value it shows
Blueprint Runtime Error: "Accessed None trying to read property SaveSettings". Blueprint: CharacterBP Function: Execute Ubergraph Character BP Graph: EventGraph Node: Print String
I’m trying to use SaveSettings to keep all game data, and so I’m not sure why I can set the volume, if it tells me that the set was invalid.
I’d love to hear any thoughts, Thanks very much!