It is unclear which projection is required here: https://geonetwork-opensource.org/manuals/3.6.x/en/user-guide/harvesting/harvesting-ogcwxs.html
The WMS should support the WGS84 projection
Is that EPSG:4326 WGS84 lat/long or CRS:84 WGS84 long/lat or even EPSG:6326