Your plugins should should be compiled for Linux 64 bits. We use the Docker image of TuttleOFX to load and process your plugins, so you can reproduce the same environment locally to ensure that your plugins are recognized.
If your plugins used shared libraries you can put them in a folder "lib" or "lib64" at the root of your archive:
Here you can upload OFX plugins to add them to the ShuttleOFX catalog.