I wanted to use some mods / fixes for Sleeping Dogs: Definitive Edition like SD-RenderTweaker, Props Fixes and Umbrella Color Variants listed here:

[url=
https://www.pcgamingwiki.com/wiki/Sleeping_Dogs:_Definitive_Edition]
https://www.pcgamingwiki.com/wiki/Sleeping_Dogs:_Definitive_Edition[/url]

This mods / fixes require the use SDK compatible executable (sdhdship.exe) of the game linked on the same site.

However when I start the game with the SDK compatible executable I get a message that says that steam_api64.dll is missing.

Is there a way to get this DLL or a way around it and use the mods / fixes?

I was having this problem too. You need to head to this page github.com / SDmodding/ and download the "Non-Steam Patch (GOG Version)" archive (and still use the SDK compatible exe.

Thank you. I will try that.