your SDK doesn't work 2021 and 2019
This is the error I get on version 2019 and the 21 is the same but with another version...
"Could not load file or assembly 'Seagull.BarTender.Print, Version=18.104.22.168, Culture=neutral, PublicKeyToken=109ff779a1b4cbc7'. An attempt was made to load a program with an incorrect format."
This is the version of the .dll your install.
Bartender DLL is x64 only. Your app is likely configured as "Any CPU" or "x86".0