I'm having problems getting the Makeshift Multiplayer mod working. Error messages mention Steam. Anyone get this working on the GOG version, or is it a Steam-only thing?

FYI here's the head of the "SMAPI-latest.txt" error log:

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[23:51:53 INFO Makeshift Multiplayer] Initializing Steam integration...
[23:51:53 ERROR Makeshift Multiplayer] Exception during update: System.TypeInitializationException: The type initializer for 'StardewValleyMP.Platforms.IPlatform' threw an exception. ---> System.DllNotFoundException: Unable to load DLL 'CSteamworks': The specified module could not be found. (Exception from HRESULT: 0x8007007E)
at Steamworks.NativeMethods.SteamAPI_InitSafe()
at Steamworks.SteamAPI.Init()
at StardewValleyMP.Platforms.SteamPlatform..ctor() in C:\Users\Chase\Desktop\StardewValley\Mods\StardewValleyMP\Platforms\SteamPlatform.cs:line 20
at StardewValleyMP.Platforms.IPlatform.makeCurrentPlatform() in C:\Users\Chase\Desktop\StardewValley\Mods\StardewValleyMP\Platforms\IPlatform.cs:line 32
at StardewValleyMP.Platforms.IPlatform..cctor() in C:\Users\Chase\Desktop\StardewValley\Mods\StardewValleyMP\Platforms\IPlatform.cs:line 10
--- End of inner exception stack trace ---