The operation being attempted requires that the st_geometry file be placed in the PostgreSQL lib directory.
Place the st_geometry file in the PostgreSQL lib directory. Ensure that the file is compatible with the specific ArcGIS and PostgreSQL versions you are using.
You can get the st_geometry.dll file (Windows) or st_geometry.so file (Linux) from My Esri.
Review the following workflows, which require that a compatible st_geometry file exist in the PostgreSQL lib directory: