I’m a pidgin user. I have used pidgin under windows 7. Recently (January 7 2019) I try to login facebook chat using pidgin, but there’s a login failed message “Failed to get sync_sequence_id”. I browse on google and I find some solution to resolve the problem. I don’t know about the technical explanation but I just replace the libfacebook.dll in C:\Program Files\Pidgin\plugins with the new one from https://github.com/dequis/purple-facebook/files/2732267/libfacebook.zip
You can follow the discussion about this problem here https://github.com/dequis/purple-facebook/issues/449
Previously, you can chat using Facebook account from pidgin in Windows operating system environment. To make it happen you need to add libjson-glib-1.0.dll to the folder C:\Program Files\Pidgin
So you need libjson-glib-1.0.dll and libfacebook.dll to login facebook chat using pidgin in windows operating system environment.
You can get libjson-glib-1.0.dll here (https://github.com/dequis/purple-facebook/releases/download/downloads/libjson-glib-1.0.dll) and take it to C:\Program Files\Pidgin
you can get libfacebook.dll here (https://github.com/dequis/purple-facebook/files/2732267/libfacebook.zip) the updated one and place it to C:\Program Files\Pidgin\plugins
happy chatting guys…. 🙂